| 1. |
- Edström, Kristina, Professor, 1958-
(författare)
-
Battery 2030+ Roadmap
- 2020
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Climate change is the biggest challenge facing the world today. Europe is committed to achieving a climate-neutral society by 2050, as stated in the European Green Deal.1 The transition towards a climate-neutral Europe requires fundamental changes in the way we generate and use energy. If batteries can be made simultaneously more sustainable, safe, ultrahigh performing, and affordable, they will be true enablers, “accelerating the shift towards sustainable and smart mobility; supplying clean, affordable and secure energy; and mobilizing industry for a clean and circular economy” - all of which are important elements of the UN Sustainable Development Goals.In other words, batteries are a key technology for battling carbon dioxide emissions from the transport, power, and industry sectors. However, to reach our sustainability goals, batteries must exhibit ultra-high performance beyond their capabilities today. Ultra-high performance includes energy and power performance approaching theoretical limits, outstanding lifetime and reliability, and enhanced safety and environmental sustainability. Furthermore, to be commercially successful, these batteries must support scalability that enables cost-effective large-scale production.BATTERY 2030+, is the large-scale, long-term European research initiative with the vision of inventing the sustainable batteries of the future, to enable Europe to reach the goals envisaged in the European Green Deal. BATTERY 2030+ is at the heart of a green and connected society.BATTERY 2030+ will contribute to create a vibrant battery research and development (R&D) community in Europe, focusing on long-term research that will continuously feed new knowledge and technologies throughout the value chain, resulting in new products and innovations. In addition, the initiative will attract talent from across Europe and contribute to ensure access to competences needed for ongoing societal transformation.The BATTERY 2030+ aims are:• to invent ultra-high performance batteries that are safe, affordable, and sustainable, witha long lifetime.• to provide new tools and breakthrough technologies to the European battery industrythroughout the value chain.• to enable long-term European leadership in both existing markets (e.g., transport andstationary storage) and future emerging sectors (e.g., robotics, aerospace, medical devices, and Internet of things)With this roadmap, BATTERY 2030+ advocates research directions based on a chemistry-neutral approach that will allow Europe to reach or even surpass its ambitious battery performance targets set in the European Strategic Energy Technology Plan (SET-Plan)3 and foster innovation throughout the battery value chain.
|
|
| 2. |
- Raymand, David, 1981-
(författare)
-
Surface and Interface Studies of ZnO using Reactive Dynamics Simulation
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- About 90% of all chemicals are produced with the help of catalysts, substances with the ability to accelerate reactions without being consumed. Metal oxides play a prominent role in catalysis, since they are able to act reversibly in many chemical processes. Zink oxide (ZnO) is used to catalyse a number of industrially important reactions. For many of these reactions water is present as a reactant, product, or byproduct. The surface structure has a significant impact on the catalytic activity. However, currently, no experimental method simultaneously offers the spatial and temporal resolution to directly follow a catalytic process. This thesis explores surface structure dependent dynamical behavior for ZnO surfaces, nanoparticles, and water interfaces, using the computational chemistry method Molecular Dynamics, which enables detailed studies of structural and dynamical processes. Quantum mechanical (QM) calculations have been performed to obtain the energetics of the materials as a function of structure. This data has been used to parametrize reactive force-fields (ReaxFF), since the catalytic processes require both far larger and longer simulations than the capabilities of QM calculations on current computers. The simulations show that when steps are present on the surface, during crystal growth of ZnO, the creation of energetically favorable structures is accelerated. At the ZnO - water interface, structures that favor hydrogen bonding is promoted. At low, monolayer, coverage water adsorbs both molecularly and dissociatively, whereas at high coverage dissociated adsorption is favored. During evaporation from the monolayers, the ratio of dissociated and molecular water is preserved. Surface steps stabilizes the dissociated state as well as increases the rate of dissociation. The dynamical properties of ZnO nanoparticles were explored using Raman measurements and simulation. In both simulation and experiment certain vibrations were suppressed in the nanoparticles, compared to bulk. The simulations show that a narrow surface region lack the bulk-specific vibrations.
|
|
| 3. |
- Adamovic, Nadja, et al.
(författare)
-
European Materials Modelling Council
- 2017
-
Ingår i: Proceedings Of The 4Th World Congress On Integrated Computational Materials Engineering (Icme 2017). - Cham : Springer Publishing Company. - 9783319578644 - 9783319578637 ; , s. 79-92
-
Konferensbidrag (refereegranskat)abstract
- The aim of the European Materials Modelling Council (EMMC) is to establish current and forward looking complementary activities necessary to bring the field of materials modelling closer to the demands of manufacturers (both small and large enterprises) in Europe. The ultimate goal is that materials modelling and simulation will become an integral part of product life cycle management in European industry, thereby making a strong contribution to enhance innovation and competitiveness on a global level. Based on intensive efforts in the past two years within the EMMC, which included numerous consultation and networking actions with representatives of all stakeholders including Modellers, Software Owners, Translators and Manufacturers in Europe, the EMMC identified and proposed a set of underpinning and enabling actions to increase the industrial exploitation of materials modelling in Europe. EMMC will pursue the following overarching objectives in order to bridge the gap between academic innovation and industrial application: enhance the interaction and collaboration between all stakeholders engaged in different types of materials modelling, including modellers, software owners, translators and manufacturers, facilitate integrated materials modelling in Europe building on strong and coherent foundations, coordinate and support actors and mechanisms that enable rapid transfer of materials modelling from academic innovation to the end users and potential beneficiaries in industry, achieve greater awareness and uptake of materials modelling in industry, in particular SMEs, elaborate Roadmaps that (i) identify major obstacles to widening the use of materials modelling and (ii) elaborate strategies to overcome them.
|
|
| 4. |
- Agosta, Lorenzo, et al.
(författare)
-
Origin of the Hydrophobic Behaviour of Hydrophilic CeO2
- 2023
-
Ingår i: Angewandte Chemie International Edition. - : Wiley-VCH Verlagsgesellschaft. - 1433-7851 .- 1521-3773. ; 62:35
-
Tidskriftsartikel (refereegranskat)abstract
- The nature of the hydrophobicity found in rare-earth oxides is intriguing. The CeO2 (100) surface, despite its strongly hydrophilic nature, exhibits hydrophobic behaviour when immersed in water. In order to understand this puzzling and counter-intuitive effect we performed a detailed analysis of the water structure and dynamics. We report here an ab-initio molecular dynamics simulation (AIMD) study which demonstrates that the first water layer, in immediate contact with the hydroxylated CeO2 surface, is responsible for the effect behaving as a hydrophobic interface with respect to the rest of the liquid water. The hydrophobicity is manifested in several ways: a considerable diffusion enhancement of the confined liquid water as compared with bulk water at the same thermodynamic condition, a weak adhesion energy and few H-bonds above the hydrophobic water layer, which may also sustain a water droplet. These findings introduce a new concept in water/rare-earth oxide interfaces: hydrophobicity mediated by specific water patterns on a hydrophilic surface.
|
|
| 5. |
- Agosta, Lorenzo, et al.
(författare)
-
Supercooled liquid-like dynamics in water near a fully hydrated titania surface : Decoupling of rotational and translational diffusion
- 2021
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 154:9
-
Tidskriftsartikel (refereegranskat)abstract
- We report an ab initio molecular dynamics (MD) simulation investigating the effect of a fully hydrated surface of TiO2 on the water dynamics. It is found that the universal relation between the rotational and translational diffusion characteristics of bulk water is broken in the water layers near the surface with the rotational diffusion demonstrating progressive retardation relative to the translational diffusion when approaching the surface. This kind of rotation-translation decoupling has so far only been observed in the supercooled liquids approaching glass transition, and its observation in water at a normal liquid temperature is of conceptual interest. This finding is also of interest for the application-significant studies of the water interaction with fully hydrated nanoparticles. We note that this is the first observation of rotation-translation decoupling in an ab initio MD simulation of water.
|
|
| 6. |
- Amici, Julia, et al.
(författare)
-
A Roadmap for Transforming Research to Invent the Batteries of the Future Designed within the European Large Scale Research Initiative BATTERY 2030
- 2022
-
Ingår i: Advanced Energy Materials. - : John Wiley & Sons. - 1614-6832 .- 1614-6840. ; 12:17
-
Forskningsöversikt (refereegranskat)abstract
- This roadmap presents the transformational research ideas proposed by "BATTERY 2030+," the European large-scale research initiative for future battery chemistries. A "chemistry-neutral" roadmap to advance battery research, particularly at low technology readiness levels, is outlined, with a time horizon of more than ten years. The roadmap is centered around six themes: 1) accelerated materials discovery platform, 2) battery interface genome, with the integration of smart functionalities such as 3) sensing and 4) self-healing processes. Beyond chemistry related aspects also include crosscutting research regarding 5) manufacturability and 6) recyclability. This roadmap should be seen as an enabling complement to the global battery roadmaps which focus on expected ultrahigh battery performance, especially for the future of transport. Batteries are used in many applications and are considered to be one technology necessary to reach the climate goals. Currently the market is dominated by lithium-ion batteries, which perform well, but despite new generations coming in the near future, they will soon approach their performance limits. Without major breakthroughs, battery performance and production requirements will not be sufficient to enable the building of a climate-neutral society. Through this "chemistry neutral" approach a generic toolbox transforming the way batteries are developed, designed and manufactured, will be created.
|
|
| 7. |
- Arismendi Arrieta, Daniel Jose, et al.
(författare)
-
H2O2(s) and H2O22H2O(s) crystals compared with ices : DFT functional assessment and D3 analysis
- 2023
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 159:19
-
Tidskriftsartikel (refereegranskat)abstract
- The H2O and H2O2 molecules resemble each other in a multitude of ways as has been noted in the literature. Here, we present density functional theory (DFT) calculations for the H2O2(s) and H2O2·2H2O(s) crystals and make selected comparisons with ice polymorphs. The performance of a number of dispersion-corrected density functionals—both self-consistent and a posteriori ones—are assessed, and we give special attention to the D3 correction and its effects. The D3 correction to the lattice energies is large: for H2O2(s) the D3 correction constitutes about 25% of the lattice energy using PBE, much more for RPBE, much less for SCAN, and it primarily arises from non-H-bonded interactions out to about 5 Å.The large D3 corrections to the lattice energies are likely a consequence of several effects: correction for missing dispersion interaction, the ability of D3 to capture and correct various other kinds of limitations built into the underlying DFT functionals, and finally some degree of cell-contraction-induced polarization enhancement. We find that the overall best-performing functionals of the twelve examined are optPBEvdW and RPBE-D3. Comparisons with DFT assessments for ices in the literature show that where the same methods have been used, the assessments largely agree.
|
|
| 8. |
- Bako, Imre, et al.
(författare)
-
Effects of H-bond asymmetry on the electronic properties of liquid water : An AIMD analysis
- 2019
-
Ingår i: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322 .- 1873-3166. ; 293
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of an asymmetric environment on the electronic properties of a water molecule in liquid water are in focus in this paper and were analysed from ab initio molecular dynamics simulations of liquid water at 300 and 350 K with the BLYP-D3 functional. We make the following observations. (1) The electronic DOS and the net molecular charge are more affected by the asymmetry of the water molecule's H-bond surroundings than by the number of H-bonded neighbours. The reverse is true for the dipole moment. (2) For all three properties, a 3-coordinated water molecule is more perturbed by accepting two H-bonds and donating one than by donating two and accepting one. (3) This order is not maintained in the calculated XES spectrum, which is less straightforward to interpret in terms of structure-property relationships than the DOS spectrum.
|
|
| 9. |
- Bakó, Imre, et al.
(författare)
-
How can we detect hydrogen bond local cooperativity in liquid water : A simulation study
- 2017
-
Ingår i: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322 .- 1873-3166. ; 245, s. 140-146
-
Tidskriftsartikel (refereegranskat)abstract
- The significant cooperative effect between water molecules substantially affects the properties of liquid water. The cooperativity of hydrogen bonds means that the hydrogen bond strength is influenced by the neighboring water molecules. Another descriptor related to cooperativity is degree correlation (or static correlation) describing the probability of hydrogen-bonded molecule pairs participating in additional hydrogen-bonds. Herein we analyze the latter one in liquid water at various temperatures and densities in a series of molecular dynamics simulations with the help of knowledge from network science. We investigated how the applied hydrogen bond criteria (energetic or geometric) influence the obtained results, and showed that the energetic criterion is much more rigorous and reliable, therefore should be used for similar studies. We found that the structure of the subsystems of water molecules with 3 and 4 hydrogen-bonds is distinctly different at low temperature, 3‑hydrogen-bonded water molecules form branched chain structures at all temperature. Deconvolution of the descriptors of the mixing pattern of water molecules according to their donor and acceptor numbers showed that species with complementary hydrogen bonding properties are likely to correlate and form H-bonds with each other, while species with similar H-bond pattern tend to avoid each other. Pearson's coefficient (global descriptor of the local cooperativity) of the studied networks suggests that at normal density the H-bonded network in liquid water can be described by an uncorrelated network.
|
|
| 10. |
- Barcaro, Giovanni, et al.
(författare)
-
Dynamical and Structural Characterization of the Adsorption of Fluorinated Alkane Chains onto CeO2
- 2018
-
Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 122:41, s. 23405-23413
-
Tidskriftsartikel (refereegranskat)abstract
- The widespread use of ceria-based materials and the need to design suitable strategies to prepare eco-friendly CeO2 supports for effective catalytic screening induced us to extend our computational multiscale protocol to the modeling of the hybrid organic/oxide interface between prototypical fluorinated linear alkane chains (polyethylene-like oligomers) and low-index ceria surfaces. The combination of quantum chemistry calculations and classical reactive molecular dynamics simulations provides a comprehensive picture of the interface and discloses, at the atomic level, the main causes of typical adsorption modes. The data show that at room temperature. a moderate. percentage` of fluorine atoms (around 25%) can enhance the interaction of the organic chains by anchoring strongly pivotal fluorines to the channels of the underneath ceria (100) surface, whereas an excessive content can remarkably reduce this interaction because of the repulsion between fluorine and the negatively charged oxygen of the surface.
|
|
| 11. |
- Bhowmik, Arghya, et al.
(författare)
-
Implications of the BATTERY 2030+ AI-Assisted Toolkit on Future Low-TRL Battery Discoveries and Chemistries
- 2022
-
Ingår i: Advanced Energy Materials. - : John Wiley & Sons. - 1614-6832 .- 1614-6840. ; 12:17
-
Forskningsöversikt (refereegranskat)abstract
- BATTERY 2030+ targets the development of a chemistry neutral platform for accelerating the development of new sustainable high-performance batteries. Here, a description is given of how the AI-assisted toolkits and methodologies developed in BATTERY 2030+ can be transferred and applied to representative examples of future battery chemistries, materials, and concepts. This perspective highlights some of the main scientific and technological challenges facing emerging low-technology readiness level (TRL) battery chemistries and concepts, and specifically how the AI-assisted toolkit developed within BIG-MAP and other BATTERY 2030+ projects can be applied to resolve these. The methodological perspectives and challenges in areas like predictive long time- and length-scale simulations of multi-species systems, dynamic processes at battery interfaces, deep learned multi-scaling and explainable AI, as well as AI-assisted materials characterization, self-driving labs, closed-loop optimization, and AI for advanced sensing and self-healing are introduced. A description is given of tools and modules can be transferred to be applied to a select set of emerging low-TRL battery chemistries and concepts covering multivalent anodes, metal-sulfur/oxygen systems, non-crystalline, nano-structured and disordered systems, organic battery materials, and bulk vs. interface-limited batteries.
|
|
| 12. |
|
|
| 13. |
|
|
| 14. |
- Castelli, Ivano E., et al.
(författare)
-
Data Management Plans : the Importance of Data Management in the BIG-MAP Project
- 2021
-
Ingår i: Batteries & Supercaps. - : John Wiley & Sons. - 2566-6223. ; 4:12, s. 1803-1812
-
Tidskriftsartikel (refereegranskat)abstract
- Open access to research data is increasingly important for accelerating research. Grant authorities therefore request detailed plans for how data is managed in the projects they finance. We have recently developed such a plan for the EU H2020 BIG-MAP project-a cross-disciplinary project targeting disruptive battery-material discoveries. Essential for reaching the goal is extensive sharing of research data across scales, disciplines and stakeholders, not limited to BIG-MAP and the European BATTERY 2030+ initiative but within the entire battery community. The key challenges faced in developing the data management plan for such a large and complex project were to generate an overview of the enormous amount of data that will be produced, to build an understanding of the data flow within the project and to agree on a roadmap for making all data FAIR (findable, accessible, interoperable, reusable). This paper describes the process we followed and how we structured the plan.
|
|
| 15. |
- Cheng, Cheng, et al.
(författare)
-
Identification of High-Performance Single-Atom MXenes Catalysts for Low-Temperature CO Oxidation
- 2019
-
Ingår i: Advanced Theory and Simulations. - : WILEY-V C H VERLAG GMBH. - 2513-0390. ; 2:8
-
Tidskriftsartikel (refereegranskat)abstract
- On the basis of first-principles calculations, Fe, Co, Ni, Cu, Zn, Ru, Rh, Ag, Ir, Pt, and Au decorated Mo2CO2-delta monolayers are investigated as potential single-atom catalyst (SAC) candidates for low-temperature CO oxidation reaction. From a first screening based on intuitive criteria concerning metal sintering, CO poisoning, and O-2 adsorption strength, the Zn/Mo2CO2-delta system is selected for further scrutiny by means of reactivity calculations for different CO concentrations. A lower barrier is found for Eley-Rideal reaction mechanism than for the Langmuir-Hinshelwood mechanism. The low Eley-Rideal barrier (0.15 eV) is attributed to the fact that the Zn atom weakens the O-O bond considerably and the electrophilic attack of CO weakens it further. The main conclusion is that this system is a promising low-temperature SAC candidate with a lower energy barrier for CO oxidation than noble metal and other 2D SAC systems investigated.
|
|
| 16. |
- Colozza, Noemi, et al.
(författare)
-
A Paper-Based Potentiometric Sensor for Solid Samples : Corrosion Evaluation of Reinforcements Embedded in Concrete Structures as a Case Study
- 2020
-
Ingår i: ChemElectroChem. - : Wiley. - 2196-0216. ; 7:10, s. 2274-2282
-
Tidskriftsartikel (refereegranskat)abstract
- Herein, we present the first paper-based device for facing one of the worldwide concerns of the Modern age: the corrosion-induced deterioration of reinforced concrete. Indeed, the monitoring of corrosion extent in reinforced concrete constructions has been acknowledged as a priority for public safety. In this work, the porosity properties of a paper-based screen-printed Ag/AgCl electrode were exploited for realising a smart analytical tool to be directly applied on the solid surface of concrete for the evaluation of corrosion. The analysis was carried out by measuring the electrochemical potential between the metallic reinforcement and the sensor, needing only 70 mu L of electrolyte solution. The sensor was firstly tested in the laboratory using reinforced concrete samples and then applied on the real outdoor artwork Music Collection Session by Arman (Milan, Italy). A summary of the main available non-destructive techniques for corrosion monitoring is reported to provide a critic overview.
|
|
| 17. |
- Colozza, Noemi, et al.
(författare)
-
Multiparametric analysis by paper-assisted potentiometric sensors for diagnostic and monitoring of reinforced concrete structures
- 2021
-
Ingår i: Sensors and actuators. B, Chemical. - : Elsevier. - 0925-4005 .- 1873-3077. ; 345
-
Tidskriftsartikel (refereegranskat)abstract
- Reinforced concrete has been employed worldwide as a leading building material for public and private structures as well as in modern sculptural art. Although the unrivalled mechanical strength and modelling versatility of this material, several interrelated processes are responsible for its progressive degradation (e.g., carbonation, penetration of aging-promoting agents), decreasing its long-last durability and representing a risk for the public security or the cultural heritage. With the aim to tackle this issue, the present work reports a novel configuration of a screen-printed sensor, obtained by the combination of flexible and robust polyester support and wax-printed filter paper device for the direct application on the concrete surface. Our sensor consists of a polyester-printed three-electrochemical cell that allows dual measurements on reinforced concrete, namely (i) the evaluation of corrosion probability of the metallic reinforcements (which outperforms the half-cell potential standard method) and (ii) the employment of a pH-sensitive iridium oxide film for the measurement of the pH of concrete. The paper was used as a porous material capable of ensuring the electrochemical connection between the Ag/AgCl printed electrode and the concrete solid matrix, acting also as a protective envelope for the electrode. After the laboratory tests, which revealed the noteworthy performances of the sensors in distinguishing among different levels of corrosion as well as measuring the pH of concrete, the developed sensor was applied for on-site measurement at the Giacomo Manzu Museum (Ardea, Italy), demonstrating its suitability for the real application to cultural heritage conservation. Overall, this easy-to-handle and non-invasive diagnostic device provides an innovative analytical approach for the on-site and prompt multiparametric monitoring of the physico-chemical phenomena that endanger the long-lasting preservation of reinforced concrete structures.
|
|
| 18. |
- Colozza, Noemi, et al.
(författare)
-
Vertical-Flow Paper Sensor for On-Site and Prompt Evaluation of Chloride Contamination in Concrete Structures
- 2021
-
Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 93:43, s. 14369-14374
-
Tidskriftsartikel (refereegranskat)abstract
- Corrosion occurring in reinforced concrete has turned into a primary concern of the current century, concrete being the most ubiquitous and predominant material used in the construction industry. Among the many interrelated processes that trigger corrosion of metallic reinforcements, the penetration of chloride ions into the concrete matrix is the most insidious threat. Herein, we developed the first electrochemical device entirely made of paper that allows for the direct, prompt, and noninvasive evaluation of free chloride ion contamination in concrete-based constructions. Our device is based on a three-layer wax-modified filter paper, consisting of two Ag/AgCl screen-printed electrodes that are interfaced by a junction pad in a sandwich-like configuration. Filter paper allows for generating a vertical-flow potentiometric device capable of measuring the electrochemical potential between two solutions containing different concentrations of chloride ions, which are separately drop-cast on the top and bottom layers. After demonstrating the analytical performance of the device, the same principle was applied to the evaluation of the chloride contents in different concrete samples, exploiting paper as a suitable interfacing material for potentiometric measurements on the cement solid surface. Laboratory-prepared concrete samples with known chloride contents were first assessed, and then, the paper-based vertical-flow device was applied to real concrete structures at the Giacomo Manzu Museum (Ardea, Italy) for the evaluation of chloride contamination caused by the proximity to the seaside. The capability of our device to provide timely warning of the risk conditions of concrete-based artifacts was demonstrated.
|
|
| 19. |
|
|
| 20. |
|
|
| 21. |
- Du, Dou, et al.
(författare)
-
From Ceria Clusters to Nanoparticles : Superoxides and Supercharging
- 2019
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:3, s. 1742-1750
-
Tidskriftsartikel (refereegranskat)abstract
- Several studies have reported a dramatically increased oxygen storage capacity (OSC) for small ceria nanoparticles (∼5 nm). Both experiments and theory have correlated this effect with superoxide ion formation. In previous studies, density functional theory (DFT) calculations with the PBE+U density functional have been used, and the obtained results were only in qualitative agreement with the experimental observations. One severe problem is the underbinding of the O2 molecule upon superoxide ion formation, which suggests that such species should not exist above room temperature. In this work, we use hybrid DFT functional to resolve this problem. We find that the discrepancy between theory and experiment originates from an incorrect estimate of the energy associated with the localized f-electrons with respect to the oxygen p-levels. By using average O2 adsorption energies from hybrid DFT calculations, extrapolated to large nanoparticles (3−10 nm), in conjunction with first-order desorption kinetics, we find that superoxide ions are indeed stable on nanosized ceria well above room temperature, in accordance with experiments.
|
|
| 22. |
- Du, Dou, 1988-
(författare)
-
Oxygen Storage Chemistry of Nanoceria
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The versatile redox chemistry of ceria (CeO2) originates from its Ce4f electron, which plays the key role in changing the oxidation state of Ce between +IV and +III. Ceria is, among other things, a material that can act as a powerful oxygen buffer with a high oxygen storage capacity (OSC). This is used in many technical applications, such as the three-way catalyst, cleaning exhausts from gasoline vehicles. This thesis is concerned with the dramatic OSC effect observed experimentally in the literature for very small ceria nanoparticles (NPs) at lower temperatures, where the effect was found to be accompanied by the formation of superoxide ions (O2–).The main aim of the thesis work was to develop strategies to allow us to discover the origin of the OSC phenomenon, and to simulate temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) experiments and collect useful mechanistic insight about these processes. Quantum-mechanical (DFT) calculations, partly with modified DFT functionals, and later augmented by microkinetic (MK) modelling building on the DFT-results, made it possible to model the large and complex NP systems needed to make detailed comparisons between theory and experiment feasible.At first, a suitable DFT functional for nanoceria was needed. We turned to hybrid functionals, and more specifically, the non-local Fock exchange contribution within the hybrid functional HSE06 was explored. The amount that gave the best overall description was determined (15%, labeled HSE06' below) and was used in subsequent studies. Moreover, an accompanying HSE06'//PBE+U computational protocol was constructed (HSE06' energies calculated for pre-optimized structures at the PBE+U level); this made it possible to use the hybrid functional for large ceria systems.With the modified HSE functional, we scrutinized a previously proposed OSC model, namely the "supercharge" model for nanoparticles loaded on the outside with superoxide ions at low-coordinated ridge sites, enabled by the oxidation of Ce3+ to Ce4+. In the previous study, adsorption energies were calculated using the PBE+U density functional, which does not give adsorption energies in agreement with experiment. With the new HSE06' functional, together with the Redhead equation, we obtained an estimated oxygen desorption peak at ca. 415 K, in much better agreement with the experimental TPD peak at 440 K. However, this calculation could still not explain the large broadening of the experimental TPD spectrum. An oxygen adsorption energy model was then formulated which took Ce coordination and superoxide ion coverage into account. With microkinetic simulations based in this energy model, we achieved a broad simulated TPD signal, which was largely in agreement with the experimental spectrum.Finally, an improved “supercharge” model was assessed concerning its ability to mimic the temperature-programmed reduction (TPR) experiments reported in the literature for H2 interacting with ceria nanoparticles. We proposed that the reduction process follows a Langmuir-Hinshelwood reaction mechanism, which gave a simulated TPR spectrum in good agreement with the experimental results.In summary, the goals listed above were achieved: we managed to simulate TPD and TPR spectra, using a DFT-based MK approach; the results were in good agreement with experiment and useful mechanistic insight about these processes and the OSC mechanism was derived from the MK simulations and the DFT analyses.
|
|
| 23. |
- Du, Dou, et al.
(författare)
-
Screened hybrid functionals applied to ceria : Effect of Fock exchange
- 2018
-
Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 97:23
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate how the redox properties of ceria are affected by the fraction of Fock exchange in screened HSE06-based hybrid density functionals, and we compare with PBE+U results, and with experiments when available. We find that using similar to 15% Fock exchange yields a good compromise with respect to structure, electronic structure, and calculated reduction energies, and represents a significant improvement over the PBE+U results. We also investigate the possibility to use a computationally cheaper HSE06//PBE+U protocol consisting of structure optimization with PBE+U, a subsequent lattice parameter rescaling step, and, finally, a single-point full hybrid calculation. We find that such a composite computational protocol works very well and yields results in close agreement with those where HSE06 was used also for the structure optimization.
|
|
| 24. |
- Du, Dou, et al.
(författare)
-
Simulated temperature programmed desorption experiments for calcined nanoceria powders
- 2020
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 384, s. 252-259
-
Tidskriftsartikel (refereegranskat)abstract
- Density functional theory calculations (DFT), coupled with microkinetic modelling, have been used to simulate Temperature Programmed Desorption (TPD) experiments for calcined ceria nanopowders with the aim to gain insight into the chemistry governing their high redox activity. Our simulations consider two main nanoparticle models. One is a perfect ceria octahedron supercharged with adsorbed oxygen molecules turned into superoxide ions, as has previously been used to explain the enhanced oxygen storage capacity (OSC) in nanoceria. The other model is a variant where we have introduced oxygen vacancies under ridge Ce ions, thereby reducing their coordination numbers to five. The results from our microkinetic modelling suggest that including such five-coordinated Ce adsorption sites results in a TPD spectrum that better matches the experimental counterpart in terms of both peak position and width. In addition, this new structural model allows for the co-existence of Ce3+ ions, superoxide ions and O-2 molecules, as seen in experiments in the literature.
|
|
| 25. |
|
|
| 26. |
- Heinen, Stefan, et al.
(författare)
-
Reducing training data needs with minimal multilevel machine learning (M3L)
- 2024
-
Ingår i: Machine Learning. - : Institute of Physics Publishing (IOPP). - 2632-2153. ; 5:2
-
Tidskriftsartikel (refereegranskat)abstract
- For many machine learning applications in science, data acquisition, not training, is the bottleneck even when avoiding experiments and relying on computation and simulation. Correspondingly, and in order to reduce cost and carbon footprint, training data efficiency is key. We introduce minimal multilevel machine learning (M3L) which optimizes training data set sizes using a loss function at multiple levels of reference data in order to minimize a combination of prediction error with overall training data acquisition costs (as measured by computational wall-times). Numerical evidence has been obtained for calculated atomization energies and electron affinities of thousands of organic molecules at various levels of theory including HF, MP2, DLPNO-CCSD(T), DFHFCABS, PNOMP2F12, and PNOCCSD(T)F12, and treating them with basis sets TZ, cc-pVTZ, and AVTZ-F12. Our M3L benchmarks for reaching chemical accuracy in distinct chemical compound sub-spaces indicate substantial computational cost reductions by factors of ∼1.01, 1.1, 3.8, 13.8, and 25.8 when compared to heuristic sub-optimal multilevel machine learning (M2L) for the data sets QM7b, QM9LCCSD (T), Electrolyte Genome Project, QM9CACESD(T), and QM9CECASD(T), respectively. Furthermore, we use M2L to investigate the performance for 76 density functionals when used within multilevel learning and building on the following levels drawn from the hierarchy of Jacobs Ladder: LDA, GGA, mGGA, and hybrid functionals. Within M2L and the molecules considered, mGGAs do not provide any noticeable advantage over GGAs. Among the functionals considered and in combination with LDA, the three on average top performing GGA and Hybrid levels for atomization energies on QM9 using M3L correspond respectively to PW91, KT2, B97D, and τ-HCTH, B3LYP*(VWN5), and TPSSH.
|
|
| 27. |
- Hermansson, Kersti, Professor
(författare)
-
DFT-based multi-scale modelling of materials and nanoparticles
- 2017
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Redox-active metal oxide surfaces and interfaces ‒ such as electrodes, catalysts, and sensors ‒ play crucial roles in our society and in the development of new materials and greener technologies. In the scientific literature, a full arsenal of experimental methods are being used to help to characterize such materials interfaces. Simultaneously, the (ever-increasing) theoretical materials studies in the literature provide structural and mechanistic information at a detail that is difficult to beat by experiments – but are the models accurate enough? There are at least two major challenges in materials modelling: (i) how to build structural models that capture the complexity and imperfections of the real systems, and (ii) how to find good enough interaction models (say a DFT functional [1] or a force-field). Here mimicking the interactions and chemical properties of materials without explicit electrons present is a formidable task, especially when the transfer of electrons is closely coupled to the material's functionality, as is the case for redox-active metal oxides.I will discuss some of our efforts in the development of a multiscale modelling approach for surfaces and interfaces of metal oxides (e.g. CeO2, ZnO, MgO) – with and without interacting molecules (e.g. O2 and water).In summary, we combine a range of theoretical methods including DFT [2], tight-binding-DFT [3], and reactive force-field simulations [4] in a consistent multi-scale approach to examine the properties of oxide nanosystems. We generate images and spectra to make direct comparisons with the experimental counterparts (e.g. IRRAS spectra [5]), but we also generate properties that cannot be measured by experiments such as the water dipole moment enhancement on a surface (often much larger [1] than in liquid water!). I will also inform about the European Materials Modelling Council (https://emmc.info/), and our efforts to promote the use and quality of materials modelling in industry; the EMMC is open to everyone interested. References[1] G. G. Kebede, D. Spångberg, P. D. Mitev, P. Broqvist, K. Hermansson, "Comparing van der Waals DFT methods for water on NaCl(001) and MgO(001), The Journal of Chemical Physics 146, 064703 (2017). [2] M. Hellström, D. Spångberg, K. Hermansson, "Treatment of Delocalized Electron Transfer in Periodic and Embedded Cluster DFT Calculations: The Case of Cu on ZnO (10-10)", Journal of Computational Chemistry 36, 2394 (2015). [3] J. Kullgren, M. J. Wolf, K. Hermansson, Ch. Köhler, B. Aradi,Th. Frauenheim, and P. Broqvist, "Self-Consistent-Charge Density-Functional Tight-Binding (SCC-DFTB) Parameters for Ceria in 0D to 3D". J. Phys. Chem. C 121, 4593−4607 (2017). [4] P. Broqvist, J. Kullgren, M. J. Wolf, A. C. T. van Duin, K. Hermansson, "A ReaxFF force-field for ceria bulk, surfaces and nanoparticles", J. Phys. Chem. C 119, 13598 (2015). [5] S. Hu, Z. Wang, A. Mattsson, L. Österlund, K. Hermansson, "Simulation of IRRAS Spectra for Molecules on Oxide Surfaces: CO on TiO2(110)", J. Phys. Chem. C 119, 5403 (2015).
|
|
| 28. |
- Hermansson, Kersti, Professor
(författare)
-
Hydrogen bonds – on the move
- 2017
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Hydrogen bonds are quite special bonds: they are strong enough to significantly modify a molecule’s properties and hold it in place in a structure, yet weak enough to be distorted or broken fairly easily by an external stimulus, an incoming reactant or a by-passing molecule. Thus, its place between the strong normal chemical bonds and the weakest van der Waals interactions makes the H-bond a very versatile and useful actor – as demonstrated by nature in numerous examples from Biology to Materials Science.This functional diversity is a unique and important feature, and an opportunity, but also a challenge since no controlled use of the remarkable properties of H-bonds can be achieved without a thorough understanding of their multi-functionality. Here computational approaches at a range of time and length scales can be of immense help as they provide results of unmatched detail, as well as the needed atomic-level understanding ‒ if the computational models and methods are accurate and realistic enough. Many such efforts can be found in the literature.*) At the same time, new powerful experimental characterization techniques emerge and new infrastructures are under development in Europe. The interplay between experiment and theory is becoming even more compelling as the dimensions of experimental and computational targets approach each other. **) *) Some published [1,2,3] and unpublished examples of our own efforts here for H-bonded systems (solutions, solids, surfaces) will also be mentioned.*) Here I will also inform about new European initiatives on this topic such as the European Materials Modelling Council. References [1] The vibrating hydroxide ion in water (Perspectives article), K. Hermansson, Ph.A. Bopp, D. Spångberg, Lj. Pejov, I. Bako, P. D. Mitev; Chemical Physics Letters 514, (2011), 1.[2] H-bond and Electric Field Correlations for Water in Highly Hydrated Crystals (invited), A. Sen, P. Mitev, A. Eriksson, K. Hermansson, Int. J. Quantum Chemistry 116, (2016), 57.[3] Comparing van der Waals DFT methods for water on NaCl(001) and MgO(001), G. G. Kebede, D. Spångberg, P.D. Mitev, P. Broqvist, and K.Hermansson, J. Chem. Phys. 146, (2017), 064703.
|
|
| 29. |
- Hermansson, Kersti, Professor
(författare)
-
Multi-Scale modelling of water and hydroxide in solids and solutions
- 2017
-
Ingår i: Contributions, Section of Natural, Mathematical and Biotechnical Sciences, MASA. - Macedonia : Macedonian Academy of Sciences and Arts. - 1857-9027 .- 1857-9949. ; 38:1, s. 17-26
-
Tidskriftsartikel (refereegranskat)abstract
- This report discusses some of the most pressing challenges that need to be overcome for computational con-densed-matter chemistry to become fully accepted, at par with experiments. The prospects are rather bright. By means of a few examples, all connected to the bound water molecule and the hydroxide ion, and their mysteries, the unique capabilities of theoretical calculations to provide new insights and sometimes even surpass experiments in accuracy, will be demonstrated.
|
|
| 30. |
- Hermansson, Kersti, Professor
(författare)
-
Multiscale modelling of metal oxide interfaces and nanoparticles
- 2017
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Redox-active metal oxide surfaces and interfaces ‒ such as electrodes, catalysts, and sensors ‒ play crucial roles in our society and in the development of new materials and greener technologies. In the scientific literature, a full arsenal of experimental methods are being used to help characterize such interfaces. At the same time, the number of theoretical studies in the literature steadily increases, providing mechanistic information at a detail that is hard to beat by experiment. Are such theoretical results accurate enough? Here the major challenges are (i) how to build a structural model that captures the complexity and imperfections of the real system at hand, and (ii) how to find an interaction model/a materials relation (say a DFT functional [1] or a force-field) that is good enough.A 5 nm metal oxide nanoparticle may be very small to an experimentalist, but it contains many thousand atoms, making standard quantum-mechanical (e.g. regular DFT) methods totally unfeasible. Can force-field calculations be used instead? Well, mimicking the interactions and chemical properties without explicit electrons present is a formidable task, especially when the transfer of electrons is closely coupled to the material's functionality, as is the case for redox-active metal oxides. I will discuss some of our efforts in the development of a multiscale modelling approach for surfaces and interfaces of metal oxides (e.g. CeO2, ZnO, MgO) – with and without interacting molecules (e.g. O2 and water).In summary, we combine a range of theoretical methods including DFT [2], tight-binding-DFT [3], and reactive force-field simulations [4] in a consistent multi-scale approach to examine the properties of oxide nanosystems. We generate images and spectra to make direct comparisons with the experimental couterparts (e.g. IRRAS spectra [5] and a new unpublished approach to predict vibrational spectra for OH-covered metal oxides), but we also generate properties that cannot be measured by experiments such as the water dipole moment enhancement on a surface (oftem much larger than in liquid water!). I will also inform about the European Materials Modelling Council (https://emmc.info/), and our efforts to promote the use of materials modelling in industry and the quality of the modelling results; the EMMC is open to everyone interested.References:[1] G. G. Kebede, D. Spångberg, P. D. Mitev, P. Broqvist, K. Hermansson, "Comparing van der Waals DFT methods for water on NaCl(001) and MgO(001), The Journal of Chemical Physics 146, 064703 (2017). [2] M. Hellström, D. Spångberg, K. Hermansson, "Treatment of Delocalized Electron Transfer in Periodic and Embedded Cluster DFT Calculations: The Case of Cu on ZnO (10-10)", Journal of Computational Chemistry 36, 2394 (2015). [3] J. Kullgren, M. J. Wolf, K. Hermansson, Ch. Köhler, B. Aradi,Th. Frauenheim, and P. Broqvist, "Self-Consistent-Charge Density-Functional Tight-Binding (SCC-DFTB) Parameters for Ceria in 0D to 3D". J. Phys. Chem. C 121, 4593−4607 (2017). [4] P. Broqvist, J. Kullgren, M. J. Wolf, A. C. T. van Duin, K. Hermansson, "A ReaxFF force-field for ceria bulk, surfaces and nanoparticles", J. Phys. Chem. C 119, 13598 (2015). [5] S. Hu, Z. Wang, A. Mattsson, L. Österlund, K. Hermansson, "Simulation of IRRAS Spectra for Molecules on Oxide Surfaces: CO on TiO2(110)", J. Phys. Chem. C 119, 5403 (2015).
|
|
| 31. |
- Hermansson, Kersti, Professor
(författare)
-
Multiscale modelling of reactive metal oxide interfaces
- 2017
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Chemically active metal oxide surfaces and interfaces ‒catalysts, sensors, electrodes‒ play crucial roles in our society and in the development of new technologies. Modelling such complex systems is by no means easy, and the computational scientist needs to make shrewd decisions about both the choice of structural model for the interface and the choice of total-energy method. This presentation concerns static and dynamic condensed-matter chemistry modelling of metal oxide surfaces, interfaces, nanoparticles. I will discuss some of our efforts to develop multiscale modelling protocols for metal oxide surfaces, nanoparticles and interfaces (e.g. CeO2 and ZnO) – with and without interacting molecules. We combine a range of theoretical methods including DFT, tight-binding-DFT, and reactive force-field models. A key question here is whether it is really possible to model redox-active metal oxides without including the electrons? Adequate models for post-processing of simulation data is as important as the data generation itself, since the post-processing links directly to experimental methods for e.g. surface characterization, such as spectra and images. I will also discuss some of our efforts in this field. Chemically active metal oxide surfaces and interfaces ‒catalysts, sensors, electrodes‒ play crucial roles in our society and in the development of new technologies. Modelling such complex systems is by no means easy, and the computational scientist needs to make shrewd decisions about both the choice of structural model for the interface and the choice of total-energy method. . I will discuss some of our efforts to develop multiscale modelling protocols for metal oxide surfaces, nanoparticles and interfaces (e.g. Ceria and ZnO) – with and without interacting molecules. We combine a range of theoretical methods including DFT, tight-binding-DFT, and reactive force-field models. A key question here is: Is it possible to model redox-active metal oxides without including the electrons? Adequate models for post-processing of simulation data is as important as the data generation itself, since the post-processing links directly to experimental methods for, e.g., surface characterization, such as spectra and images. I will also discuss some of our efforts in this field.References: [1] M. Hellström, K. Jorner, M. Bryngelsson, S.E. Huber, J. Kullgren, Th. Frauenheim, P. Broqvist, "An SCC-DFTB Repulsive Potential for Various ZnO Polymorphs and the ZnO-Water System", J. Phys. Chem. C, 2013, 117, 17004.[2] P. Broqvist, J. Kullgren, M. J. Wolf, A. C. T. van Duin, K. Hermansson, "A ReaxFF force-field for ceria bulk, surfaces and nanoparticles", J. Phys. Chem. C, 2015, 119, 13598.[3] M. Hellström, D. Spångberg, K. Hermansson, "Treatment of Delocalized Electron Transfer in Periodic and Embedded Cluster DFT Calculations: The Case of Cu on ZnO (10-10)", Journal of Computational Chemistry, 2015, 36, 2394.[4] S. Hu, Z. Wang, A. Mattsson, L. Österlund, K. Hermansson, "Simulation of IRRAS Spectra for Molecules on Oxide Surfaces: CO on TiO2(110)", J. Phys. Chem. C, 2015, 119, 5403.
|
|
| 32. |
- Herschend, Björn, 1976-
(författare)
-
Combined Molecular Dynamics and Embedded-Cluster Calculations in Metal Oxide Surface Chemistry
- 2005
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development and improvement of the functionality of metal oxides in heterogeneous catalysis and other surface chemical processes can greatly benefit from an atomic-level understanding of the surface chemistry. Atomistic calculations such as quantum mechanical (QM) calculations and molecular dynamics (MD) simulations can provide highly detailed information about the atomic and electronic structure, and constitute valuable complements to experimental surface science techniques.In this thesis, an embedded-cluster approach for quantum mechanical calculations has been developed to model the surface chemistry of metal oxides. In particular, CO adsorption on the MgO(001) and CeO2(110) surfaces as well as O vacancy formation at the CeO2(110) surface have been investigated. The cluster model has been thoroughly tested by comparison with electronic structure calculations for the periodic slab model.The chemical implications of distorted surface structures arising from the surface dynamics have been investigated by combining the QM embedded-cluster calculations with force-field based MD simulations. Here QM embedded-cluster calculations were performed using surface structures sampled from the MD simulations.This combined MD+QM embedded-cluster procedure was applied to the CO adsorption on MgO(001) at 50 K and the O vacancy formation on CeO2(110) at 300 K. Significant thermal variations of the CO adsorption energy and the O vacancy formation energy were observed. It was found that these variations could be estimated using the force field of the MD simulation as an interaction model. With this approach, the QM results were extrapolated to higher temperature and doped systems.
|
|
| 33. |
- Karandashev, Konstantin, et al.
(författare)
-
Evolutionary Monte Carlo of QM Properties in Chemical Space : Electrolyte Design
- 2023
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 19:23, s. 8861-8870
-
Tidskriftsartikel (refereegranskat)abstract
- Optimizing a target function over the space of organic molecules is an important problem appearing in many fields of applied science but also a very difficult one due to the vast number of possible molecular systems. We propose an evolutionary Monte Carlo algorithm for solving such problems which is capable of straightforwardly tuning both exploration and exploitation characteristics of an optimization procedure while retaining favorable properties of genetic algorithms. The method, dubbed MOSAiCS (Metropolis Optimization by Sampling Adaptively in Chemical Space), is tested on problems related to optimizing components of battery electrolytes, namely, minimizing solvation energy in water or maximizing dipole moment while enforcing a lower bound on the HOMO–LUMO gap; optimization was carried out over sets of molecular graphs inspired by QM9 and Electrolyte Genome Project (EGP) data sets. MOSAiCS reliably generated molecular candidates with good target quantity values, which were in most cases better than the ones found in QM9 or EGP. While the optimization results presented in this work sometimes required up to 106 QM calculations and were thus feasible only thanks to computationally efficient ab initio approximations of properties of interest, we discuss possible strategies for accelerating MOSAiCS using machine learning approaches.
|
|
| 34. |
- Kebede, Getachew, et al.
(författare)
-
Fifty Shades of Water : Benchmarking DFT Functionals against Experimental Data for Ionic Crystalline Hydrates
- 2019
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 15:1, s. 584-594
-
Tidskriftsartikel (refereegranskat)abstract
- We propose that crystalline ionic hydrates constitute a valuable resource for benchmarking theoretical methods for aqueous ionic systems. Many such structures are known from the experimental literature, and they contain a large variety of water–water and ion–water structural motifs. Here we have collected a data set (CRYSTALWATER50) of 50 structurally unique "in-crystal" water molecules, involved in close to 100 nonequivalent O–H···O hydrogen bonds. A dozen well-known DFT functionals were benchmarked with respect to their ability to describe these experimental structures and their OH vibrational frequencies. We find that the PBE, RPBE-D3, and optPBE-vdW methods give the best H-bond distances and that anharmonic OH frequencies generated from B3LYP//optPBE-vdW energy scans outperform the other methods, i.e., here we performed B3LYP energy scans along the OH stretching coordinate while the rest of the structure was kept fixed at the optPBE-vdW-optimized positions.
|
|
| 35. |
- Kebede, Getachew, et al.
(författare)
-
Hydrogen-Bond Relations for Surface OH Species
- 2018
-
Ingår i: The Journal of Physical Chemistry C. - Uppsala : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:9, s. 4849-4858
-
Recension (refereegranskat)abstract
- This paper concerns thin water films and their hydrogen-bond patterns on ionic surfaces. As far as we are aware, this is the first time H-bond correlations for surface water and hydroxide species are presented in the literature while hydrogen-bond relations in the solid state have been scrutinized for at least five decades. Our data set, which was derived using density functional theory, consists of 116 unique surface OH groups–intact water molecules as well as hydroxides–on MgO(001), CaO(001) and NaCl(001), covering the whole range from strong to weak to no H-bonds. The intact surface water molecules are found to always be redshifted with respect to the gas-phase water OH vibrational frequency, whereas the surface hydroxide groups are either redshifted (OsH) or blueshifted (OHf) compared to the gas-phase OH– frequency. The surface H-bond relations are compared with the traditional relations for bulk crystals. We find that the “ν(OH) vs R(H···O)” correlation curve for surface water does not coincide with the solid state curve: it is redshifted by about 200 cm–1 or more. The intact water molecules and hydroxide groups on the ionic surfaces essentially follow the same H-bond correlation curve.
|
|
| 36. |
- Kebede, Getachew, et al.
(författare)
-
OH
- 2017
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 37. |
- Kebede, Getachew, et al.
(författare)
-
Red-shifting and blue-shifting OH groups on metal oxide surfaces : towards a unified picture
- 2018
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 20:18, s. 12678-12687
-
Tidskriftsartikel (refereegranskat)abstract
- We analyse the OH vibrational signatures of water molecules and hydroxide ions on thin water films on MgO(001) and CaO(001), using DFT-generated anharmonic potential energy surfaces. We find that the OH stretching frequencies of intact water molecules on the surface are always downshifted with respect to the gas-phase species while the OH– groups are either upshifted or downshifted. Despite these differences, the main characteristics of the frequency shifts for all three types of surface OH groups (OHw, OsH and OHf) can be accounted for by one unified expression involving the in situ electric field from the surrounding environment, and the molecular properties of the vibrating species (H2O or OH–). The origin behind the different red- and blueshift behaviour can be traced back to the fact that the molecular dipole moment of a gas-phase water molecule increases when an OH bond is stretched, but the opposite is true for the hydroxide ion. We propose that familiarity with the relations presented here will help surface scientists in the interpretation of vibrational OH spectra for thin water films on ionic crystal surfaces.
|
|
| 38. |
- Kebede, Getachew
(författare)
-
Water in and on ionic materials : Structure, energetics, and vibrations
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many chemical and physical phenomena in nature, in industrial processes, and in our daily lives take place at water/solid interfaces. The aim of this thesis is to further our knowledge of such processes at a molecular level. Here theoretical calculations can provide new insights about molecular bonding, structure and dynamics and how these respond to the perturbations from the surroundings. Coalculations can also yield for example vibrational spectra to be directly compared with experimental ones and help in the interpretation. This thesis describes the results of quantum-mechanical and quantum-dynamical studies of water properties on ionic surfaces [NaCl(001), MgO(001) and CaO(001)] and in ionic hydrates [e.g Na2CO3∙10H2O, MgSO4∙11H2O, Al(NO3)3∙9H2O] with especial emphases on surface and interface systems. In particular, calculations of binding energies, OH stretching frequencies, in situ electric field, dipole moments and intra/intermolecular OH distances were performed and analyzed to probe the strength of the water–environment interplay and to disentangle the components of the perturbation. Furthermore, validation of a range of dispersion-inclusive DFT methods for binding energies of interface water and structure and vibrational properties of water in condensed systems also constitutes part of the thesis.Two correlations among the investigated properties were established and extensively explored: (i) OH stretching frequency vs. H-bond distance to characterize the H-bond strength and patterns on the surfaces and (ii) OH stretching frequency vs. local electric field to understand the effect of the water/hydroxide environment on the calculated gas-to-bound OH frequency shift behaviour. It was found that both the intact and dissociated water molecules on MgO(001) and CaO(001) follow essentially the same frequency-distance correlations. However, if the frequency is instead correlated against the in situ electric field from the environment, water and hydroxide ion follow different “frequency vs. field” curves. Both water and hydroxide curves, however, can be described by the same model, namely by an electrostatic dipole model presented in the thesis. The gas-to-surface frequency shifts can be traced back to the competition between the signs and magnitudes of the permanent and induced dipole derivatives along the stretching coordinate. Furthermore, the “frequency vs. field” model offers useful insights into the frequency shifts of various surface H-bond motifs on the H2O/MgO interface induced by the adsorption of multilayer cold water.
|
|
| 39. |
- Kettner, Miroslav, et al.
(författare)
-
Anion-mediated electronic effects in reducible oxides : Tuning the valence band of ceria via fluorine doping
- 2019
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 151:4
-
Tidskriftsartikel (refereegranskat)abstract
- Combining experimental spectroscopy and hybrid density functional theory calculations, we show that the incorporation of fluoride ions into a prototypical reducible oxide surface, namely, ceria(111), can induce a variety of nontrivial changes to the local electronic structure, beyond the expected increase in the number of Ce3+ ions. Our resonant photoemission spectroscopy results reveal new states above, within, and below the valence band, which are unique to the presence of fluoride ions at the surface. With the help of hybrid density functional calculations, we show that the different states arise from fluoride ions in different atomic layers in the near surface region. In particular, we identify a structure in which a fluoride ion substitutes for an oxygen ion at the surface, with a second fluoride ion on top of a surface Ce4+ ion giving rise to F 2p states which overlap the top of the O 2p band. The nature of this adsorbate F--Ce4+ resonant enhancement feature suggests that this bond is at least partially covalent. Our results demonstrate the versatility of anion doping as a potential means of tuning the valence band electronic structure of ceria.
|
|
| 40. |
|
|
| 41. |
- Kim, Byung-Hyun, et al.
(författare)
-
Indirect-to-Direct Band Gap Transition of Si Nanosheets : Effect of Biaxial Strain
- 2018
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:27, s. 15297-15303
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of biaxial strain on the band structure of two-dimensional silicon nanosheets (Si NSs) with (111), (110), and (001) exposed surfaces was investigated by means of density functional theory calculations. For all the considered Si NSs, an indirect-to-direct band gap transition occurs as the lateral dimensions of Si NSs increase; that is, increasing lateral biaxial strain from compressive to tensile always enhances the direct band gap characteristics. Further analysis revealed the mechanism of the transition which is caused by preferential shifts of the conduction band edge at a specific k-point because of their bond characteristics. Our results explain a photoluminescence result of the (111) Si NSs [U. Kim et al., ACS Nano 2011,.5, 2176-2181] in terms of the plausible tensile strain imposed in the unoxidized inner layer by surface oxidation.
|
|
| 42. |
- Kim, Byung-Hyun, et al.
(författare)
-
Multiscale Modeling of Agglomerated Ceria Nanoparticles : Interface Stability and Oxygen Vacancy Formation
- 2019
-
Ingår i: Frontiers in Chemistry. - : FRONTIERS MEDIA SA. - 2296-2646. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- The interface formation and its effect on redox processes in agglomerated ceria nanoparticles (NPs) have been investigated using a multiscale simulation approach with standard density functional theory (DFT), the self-consistent-charge density functional tight binding (SCC-DFTB) method, and a DFT-parameterized reactive force-field (ReaxFF). In particular, we have modeled Ce40O80 NP pairs, using SCC-DFTB and DFT, and longer chains and networks formed by Ce40O80 or Ce132O264 NPs, using ReaxFF molecular dynamics simulations. We find that the most stable {111}/{111} interface structure is coherent whereas the stable {100}/{100} structures can be either coherent or incoherent. The formation of {111}/{111} interfaces is found to have only a very small effect on the oxygen vacancy formation energy, E-vac. The opposite holds true for {100}/{100} interfaces, which exhibit significantly lower E-vac values than the bare surfaces, despite the fact that the interface formation eliminates reactive {100} facets. Our results pave the way for an increased understanding of ceria NP agglomeration.
|
|
| 43. |
|
|
| 44. |
- Kocmaruk, Bojana, 1994-, et al.
(författare)
-
Toward an efficient f-in-core/f-in-valence switchable description for DFTB calculations of Ce 4f states in ceria
- 2023
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 158:5
-
Tidskriftsartikel (refereegranskat)abstract
- A computational protocol is developed for efficient studies of partially reduced redox-active oxides using the self-consistent charge density functional tight-binding method. The protocol is demonstrated for ceria, which is a prototypical reducible oxide material. The underlying idea is to achieve a consistent (and harmonized) set of Slater-Koster (SK) tables with connected repulsive potentials that enable switching on and off the in-valence description of the Ce 4f states without serious loss of accuracy in structure and energetics. The implicit treatment of the Ce 4f states, with the use of f-in-core SK-tables, is found to lead to a significant decrease in computational time. More importantly, it allows for explicit control of the oxidation states of individual Ce atoms. This makes it possible to "freeze " the electronic configuration, thereby allowing the exploration of the energetics for various meta-stable configurations. We anticipate that the outlined strategy can help to shed light on the interplay between the size, shape, and redox activity for nanoceria and other related materials.
|
|
| 45. |
|
|
| 46. |
|
|
| 47. |
- Kullgren, Jolla, 1978-, et al.
(författare)
-
Water in Crystals : A Database for ML and a Knowledge Base for Vibrational Prediction
- 2023
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:28, s. 13740-13750
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrate crystals are excellent reference systems to learnaboutaqueous systems. We have created a database of density functionaltheory (DFT)-optimized (optPBE-vdW) structures and vibrational frequenciesfor 101 crystalline hydrate and hydroxide bulk systems and over 300unique oscillators and use it to explore and discuss the tradeoffbetween prediction accuracy and insight. Starting from a machine-learninggeometrical descriptor, we gradually include more physics/chemistryflavor in the descriptor and examine how the frequency predictionpower varies. The most accurate models are the machine-learned model(of modest insight) and a physically motivated model containing theelectric field and field gradient. Furthermore, detailed comparisonswith experimental correlations show that, where available data exists,our DFT results largely overlap with the experiment. A small blind-testshowed that our machine-learned (ML) descriptor model can be usedto predict experimental vibrational frequencies based only on theexperimental structures and our best-regressed model, with encouragingresults.
|
|
| 48. |
- Magdau, Ioan-Bogdan, et al.
(författare)
-
Machine learning force fields for molecular liquids : Ethylene Carbonate/Ethyl Methyl Carbonate binary solvent
- 2023
-
Ingår i: npj Computational Materials. - : Springer Nature. - 2057-3960. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Highly accurate ab initio molecular dynamics (MD) methods are the gold standard for studying molecular mechanisms in the condensed phase, however, they are too expensive to capture many key properties that converge slowly with respect to simulation length and time scales. Machine learning (ML) approaches which reach the accuracy of ab initio simulation, and which are, at the same time, sufficiently affordable hold the key to bridging this gap. In this work we present a robust ML potential for the EC:EMC binary solvent, a key component of liquid electrolytes in rechargeable Li-ion batteries. We identify the necessary ingredients needed to successfully model this liquid mixture of organic molecules. In particular, we address the challenge posed by the separation of scale between intra- and inter-molecular interactions, which is a general issue in all condensed phase molecular systems.
|
|
| 49. |
- Meier de Andrade, Ageo, 1990-, et al.
(författare)
-
Lignin Intermediates on Palladium : Insights into Keto-Enol Tautomerization from Theoretical Modelling
- 2020
-
Ingår i: ChemSusChem. - : John Wiley & Sons. - 1864-5631 .- 1864-564X. ; 13:24, s. 6574-6581
-
Tidskriftsartikel (refereegranskat)abstract
- It has been suggested in the literature that keto-to-enol tautomerization plays a vital role for lignin fragmentation under mild conditions. On the other hand, previous modelling has shown that the adsorbed keto form is more stable than enol on the Pd(111) catalyst. The current density functional theory study of lignin model molecules shows that, in the gas-phase, keto is more stable than enol, but on the Pd surface, we find enol conformers that are at least as stable as keto. This supports the experimental result that the favourable reaction pathway for lignin depolymerization involves keto-enol tautomerization. An energy decomposition analysis gives insights concerning the origin of the fine energy balance between the keto and enol forms, where the molecule–surface interaction (−7 eV) and the molecular strain energy (+3 eV) are the main contributors to the adsorption energy.
|
|
| 50. |
|
|
