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| 2. |
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| 3. |
- Du, Dou, 1988-
(författare)
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Oxygen Storage Chemistry of Nanoceria
- 2019
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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.
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| 4. |
- Gajewski, Grzegorz, et al.
(författare)
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2D calculation of anharmonic OH vibrations in a layered hydroxide crystal
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 129:6, s. 064502-
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Tidskriftsartikel (refereegranskat)abstract
- Anharmonicvibrational frequencies for the Raman-active (A1g) and the IR-active (A2u)modes have been calculated for the LiOH crystal within aplane-wave density functional theory (DFT) framework. We find that atwo-dimensional quantum-mechanical vibrational approach, allowing for anharmonic coupling between symmetricand antisymmetric OH stretching modes, produces OH frequencies—both absolute frequenciesand gas-to-solid frequency shifts—in good agreement with experiment. Remaining errorsin the absolute frequencies are largely a consequence of theDFT model chosen. A one-dimensional normal-mode following vibrational treatment, onthe other hand, fails to reproduce both absolute anharmonic frequenciesand gas-to-solid frequency shifts.
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| 5. |
- Imani, Roghayeh, et al.
(författare)
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Unravelling in-situ formation of highly active mixed metal oxide CuInO2 nanoparticles during CO2 electroreduction
- 2018
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Ingår i: Nano Energy. - : ELSEVIER SCIENCE BV. - 2211-2855 .- 2211-3282. ; 49, s. 40-50
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Tidskriftsartikel (refereegranskat)abstract
- Technologies and catalysts for converting carbon dioxide (CO2) to immobile products are of high interest to minimize greenhouse effects. Copper(I) is a promising catalytic active state of copper but hampered by the inherent instability in comparison to copper(II) or copper(0). Here, we report a stabilization of the catalytic active state of copper(I) by the formation of a mixed metal oxide CuInO2 nanoparticle during the CO2 electroreduction. Our result shows the incorporation of nanoporous Sn:In2O3 interlayer to Cu2O pre-catalyst system lead to the formation of CuInO2 nanoparticles with remarkably higher activity for CO2 electroreduction at lower overpotential in comparison to the conventional Cu nanoparticles derived from sole Cu2O. Operando Raman spectroelectrochemistry is employed to in-situ monitor the process of nanoparticles formation during the electrocatalytic process. The experimental data are collaborated with DFT calculations to provide insight into the electro-formation of the type of Cu-based mixed metal oxide catalyst during the CO2 electroreduction, where a formation mechanism via copper ion diffusion across the substrate is suggested.
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| 6. |
- Kebede, Getachew, et al.
(författare)
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Fifty Shades of Water : Benchmarking DFT Functionals against Experimental Data for Ionic Crystalline Hydrates
- 2019
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 15:1, s. 584-594
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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.
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| 7. |
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| 8. |
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| 9. |
- Kebede, Getachew, et al.
(författare)
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Hydrogen-Bond Relations for Surface OH Species
- 2018
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Ingår i: The Journal of Physical Chemistry C. - Uppsala : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:9, s. 4849-4858
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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.
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| 10. |
- Kebede, Getachew, et al.
(författare)
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OH
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 11. |
- Kebede, Getachew, et al.
(författare)
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Red-shifting and blue-shifting OH groups on metal oxide surfaces : towards a unified picture
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 20:18, s. 12678-12687
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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.
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| 12. |
- Kersti, Hermansson, et al.
(författare)
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The vibrating hydroxide ion in water
- 2011
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 514:1-3, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- The OH− ion in water is studied using a CPMD/BLYP + QMelectronic + QMvibrational approach. The ion resides in a cage of water molecules, which are H-bonded among each other, and pinned by H-bonding to the ion’s O atom. The water network keeps the ‘on-top’ water in place, despite the fact that this particular ion-water pair interaction is non-binding. The calculated OH− vibrational peak maximum is at ∼3645 cm−1 (experiment ∼3625 cm−1) and the shift with respect to the gas-phase is ∼ +90 cm−1 (experiment +70 cm−1). The waters molecules on each side of the ion (O and H) induce a substantial OH− vibrational blueshift, but the net effect is much smaller than the sum. A parabolic ‘frequency-field’ relation qualitatively explains this non-additivity. The calculated ‘in-liquid’ ν(OH−) anharmonicity is 85 cm−1.
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| 13. |
- Krishna, Akshay A. K., et al.
(författare)
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CCS : A software framework to generate two-body potentials using Curvature Constrained Splines
- 2021
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 258
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Tidskriftsartikel (refereegranskat)abstract
- We have developed an automated and efficient scheme for the fitting of data using Curvature Constrained Splines (CCS), to construct accurate two-body potentials. The approach enabled the construction of an oscillation-free, yet flexible, potential. We show that the optimization problem is convex and that it can be reduced to a standard Quadratic Programming (QP) problem. The improvements are demonstrated by the development of a two-body potential for Ne from ab initio data. We also outline possible extensions to the method.Program summaryProgram Title: CCSCPC Library link to program files: http://dx.doi.org/10.17632/7dt5nzxgbs.1Developer’s repository link: http://github.com/aksam432/CCSLicensing provisions: GPLv3Programming language: PythonExternal routines/libraries: NumPy, matplotlib, ASE, CVXOPTNature of problem: Ab initio quantum chemistry methods are often computationally very expensive. To alleviate this problem, the development of efficient empirical and semi-empirical methods is necessary. Two-body potentials are ubiquitous in empirical and semi-empirical methods.Solution method: The CCS package provides a new strategy to obtain accurate two body potentials. The potentials are described as cubic splines with curvature constraints.
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| 14. |
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| 15. |
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| 16. |
- Kullgren, Jolla, 1978-, et al.
(författare)
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DFT-based Monte Carlo Simulations of Impurity Clustering at CeO2(111)
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 121:28, s. 15127-15134
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Tidskriftsartikel (refereegranskat)abstract
- The interplay between energetics and entropy in determining defect distributions at ceria(111) is studied using a combination of DFT+U and lattice Monte Carlo simulations. Our main example is fluorine impurities, although we also present preliminary results for surface hydroxyl groups. A simple classical force-field model was constructed from a training set of DFT+U data for all symmetrically inequivalent (F-)(n)(Ce3+)(n) nearest-neighbor clusters with n = 2 or 3. Our fitted model reproduces the DFT energies well. We find that for an impurity concentration of 15% at 600 K, straight and hooked linear fluorine clusters are surprisingly abundant, with similarities to experimental STM images from the literature. We also find that with increasing temperature the fluorine cluster sizes show a transition from being governed by an attractive potential to being governed by a repulsive potential as a consequence of the increasing importance of the entropy of the Ce3+ ions. The distributions of surface hydroxyl groups are noticeably different.
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| 17. |
- Langhammer, David, 1991-, et al.
(författare)
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SO2 adsorption on rutile TiO2(110) : An infrared reflection-absorption spectroscopy and density functional theory study
- 2018
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Ingår i: Surface Science. - : Elsevier. - 0039-6028 .- 1879-2758. ; 677, s. 46-51
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of SO2 on single crystalline TiO2(110) has been investigated by means of polarized infrared reflection-absorption spectroscopy (IRRAS) experiments and density functional theory (DFT) calculations. IR absorption bands were detected at 1324 cm-1 and 985 cm-1 with p-polarized light incident along both the [110] and [001] crystallographic directions at 123 K. When the temperature was increased to 153 K, the peak at 1324 cm-1 disappears, while a new, weak band appears at 995 cm-1. Simultaneously, a band at 995 cm-1 also emerges with s-polarized light along the [110] direction. Based on the symmetry properties of the IRRAS spectra and accompanying ab initio simulations of the spectra employing a three layer model (vacuum-adsorbate-substrate), it is shown that the low temperature absorption IRRAS bands can be attributed to an SO3-like adsorbate structure. This is also the most stable adsorption structure (Ead = - 0.58 eV) on the stoichiometric surface. The combined IRRAS and DFT results show that the band appearing at 995 cm-1 is associated with a surface sulfite specie which is stabilized by residual surface water. The DFT calculations also revealed that a stable adsorption structure exists on a reduced TiO2 surface, where SO2 binds strongly to an oxygen vacancy site. It is suggested that this is an intermediate that form surface sulfate upon further reactions with water, although it was not observed on the stoichiometric surface studied in this work.
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| 18. |
- Mitev, Pavlin D., et al.
(författare)
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Anharmonic OH vibrations in brucite: Small pressure-induced redshift in the range 0–22 GPa
- 2009
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Ingår i: American Mineralogist. - : Mineralogical Society of America. - 0003-004X .- 1945-3027. ; 94:11-12, s. 1687-1697
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Tidskriftsartikel (refereegranskat)abstract
- The uncoupled anharmonic OH-stretching vibrational frequency for the layered mineral Mg(OH)2(brucite) has been calculated in the pressure range 0(DFT) calculations were performed, followed by quantum-mechanical vibrational energy calculations.The following findings emerged: (1) The calculated d with the experimental literature value [taken as the average between the Raman and IR-measured slopes for Mg(OH) much smaller than that of traditional H-bond correlation curves in the literature. (3) The main origin of the small d are pressed toward each other. (4) At high pressure, the OH with respect to the variation of the D quadrupole coupling constant is approximately –1 kHz/GPa. −22 GPa. Quantum-mechanical electronic structureν(OH)/dP slope is –4 cm–1/GPa, in agreement2]. (2) The calculated ν(OH) vs. R(O···O) correlation is linear and the slope isν/dP and dν/dR(O···O) slopes is the small electric field variation as the mineral layers− ions show some tendency to be tiltedc axis, and a larger tilt angle leads to a larger ν(OH) downshift. (5) The pressure variation of the D quadrupole coupling constant is approximately –1 kHz/GPa.
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| 19. |
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| 20. |
- Mitev, Pavlin D., et al.
(författare)
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Different structures give similar vibrational spectra : The case of OH- in aqueous solution
- 2013
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 138:6, s. 064503-
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Tidskriftsartikel (refereegranskat)abstract
- We have calculated the anharmonic OH-(aq) vibrational spectrum in aqueous solution with a "classical Monte Carlo simulation + QM/MM + vibrational" sequential approach. A new interaction model was used in the Monte Carlo simulations: a modified version of the charged-ring hydroxide-water model from the literature. This spectrum is compared with experiment and with a spectrum based on CPMD-generated structures, and the hydration structures and H-bonding for the two models are compared. We find that: (i) the solvent-induced frequency shift as well as the absolute OH- frequency are in good agreement with experiment using the two models; (ii) the Raman and IR bands are very similar, in agreement with experiment; (iii) the hydration structure and H-bonding around the ion are very different with the two ion-water interaction models (charged-ring and CPMD); (iv) a cancellation effect between different regions of the hydration shell makes the total spectra similar for the two interaction models, although their hydration structures are different; (v) the net OH- frequency shift is a blueshift of about + 80 cm(-1) with respect to frequency of the gas-phase ion.
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| 21. |
- Mitev, Pavlin D., et al.
(författare)
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Large polarization but small electron transfer for water around Al3+ in a highly hydrated crystal
- 2014
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:20, s. 9351-9363
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Tidskriftsartikel (refereegranskat)abstract
- Precise molecular-level information on the water molecule is precious, since it affects our interpretation of the role of water in a range of important applications of aqueous media. Here we propose that electronic structure calculations for highly hydrated crystals yield such information. Properties of nine structurally different water molecules (19 independent O center dot center dot center dot O hydrogen bonds) in the Al(NO3)(3) center dot 9H(2)O crystal have been calculated from DFT calculations. We combine the advantage of studying different water environments using one and the same compound and method (instead of comparing a set of independent experiments, each with its own set of errors) with the advantage of knowing the exact atomic positions, and the advantage of calculating properties that are difficult to extract from experiment. We find very large Wannier dipole moments for H2O molecules surrounding the cations: 4.0-4.3 D (compared to our calculated value of 1.83 D in the gas phase). These are induced by the ions and the H-bonds, while other water interactions and the relaxation of the internal water geometry in fact decrease the dipole moments. We find a good correlation between the water dipole moment and the O center dot center dot center dot O distances, and an even better (non-linear) correlation with the average electric field over the molecule. Literature simulation data for ionic aqueous solutions fit quite well with our crystalline `dipole moment vs. O center dot center dot center dot O distance' curve. The progression of the water and cation charges from ` small clusters double right arrow large clusters double right arrow the crystal' helps explain why the net charges on all the water molecules are so small in the crystal.
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| 22. |
- Mitev, Pavlin D., Dr. 1974-, et al.
(författare)
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Space-Resolved OH Vibrational Spectra of the Hydration Shell around CO2
- 2021
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 125:51, s. 13886-13895
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Tidskriftsartikel (refereegranskat)abstract
- The CO2 molecule is weakly bound in water. Here we analyze the influence of a dissolved CO2 molecule on the structure and OH vibrational spectra of the surrounding water. From the analysis of ab initio molecular dynamics simulations (BLYP-D3) we present static (structure, coordination, H-bonding, tetrahedrality) and dynamical (OH vibrational spectra) properties of the water molecules as a function of distance from the solute. We find a weakly oscillatory variation (“ABBA”) in the ‘solution minus bulk water’ spectrum. The origin of these features can largely be traced back to solvent–solute hard-core interactions which lead to variations in density and tetrahedrality when moving from the solute’s vicinity out to the bulk region. The high-frequency peak in the solute-affected spectra is specifically analyzed and found to originate from both water OH groups that fulfill the geometric H-bond criteria, and from those that do not (dangling ones). Effectively, neither is hydrogen-bonded.
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| 23. |
- Mitev, Pavlin D., et al.
(författare)
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Vibrational models for a crystal with 36 water molecules in the unit cell : IR spectra from experiment and calculation
- 2015
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 17:16, s. 10520-10531
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Tidskriftsartikel (refereegranskat)abstract
- We present experimental and calculated IR spectra of the water molecules in crystalline aluminium nitrate nonahydrate and a method to generate a realistic and well resolved isotope-isolated spectrum from periodic DFT calculations. Our sample crystal contains 18 structurally different OH groups and is a perfect benchmark compound to validate vibrational models and the structure-property relationship of bound water molecules. FTIR spectra (ATR technique) were recorded for the Al(NO3)(3)center dot 9H(2)O crystal at 138 and 298 K, and due to a multitude of OH contributions and couplings, they are naturally poorly resolved and yield a broad OH band in the range 3500 to 2700 cm(-1) at both temperatures. Isotope-isolated IR spectra have the clear advantage over non-deuterated spectra that they are better resolved and easier to interpret - here we have extended the experimental study by simulating the isotope-isolated IR spectrum, using PBE-D2 and auxiliary B3LYP calculations and an anharmonic OH vibrational model. We find excellent agreement between the shapes and frequency ranges of the experimental and calculated OH spectral bands. We make use of four different vibrational models: (i) a harmonic lattice-dynamical model for the isotope-isolated crystal with 1 H among 71 D, (ii) a harmonic lattice-dynamical model for the normal undeuterated crystal involving all the vibrational couplings, (iii) a harmonic 1-dimensional uncoupled OH vibrational model, and (iv) the anharmonic variant of the previous model, which yields the final spectrum. We also use the individual frequencies, resolved by the calculations, to quantify new or extended relationships involving OH frequencies versus local electric fields and H-bond distances. We explore the correlation between OH frequency and molecular dipole moment for bound water molecules.
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| 24. |
- Probst, Michael, et al.
(författare)
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A gold cyano complex in nitromethane : MD simulation and X-ray diffraction
- 2012
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 539, s. 24-29
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Tidskriftsartikel (refereegranskat)abstract
- The solvation structure around the dicyanoaurate(I) anion (Au(CN)(2)) in a dilute nitromethane (CH3NO2) solution is presented from X-ray diffraction measurements and molecular dynamics simulation (NVT ensemble, 460 nitromethane molecules at room temperature). The simulations are based on a new solute-solvent force-field fitted to a training set of quantum-chemically derived interaction energies. Radial distribution functions from experiment and simulation are in good agreement. The solvation structure has been further elucidated from MD data. Several shells can be identified. We obtain a solvation number of 13-17 nitromethane molecules with a strong preference to be oriented with their methyl groups towards the solute. (C) 2012 Elsevier B.V. All rights reserved.
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| 25. |
- Quaranta, Vanessa, et al.
(författare)
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Maximally resolved anharmonic OH vibrational spectrum of the water/ZnO(10(1)over-bar0) interface from a high-dimensional neural network potential
- 2018
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Ingår i: Journal of Chemical Physics. - : AMER INST PHYSICS. - 0021-9606 .- 1089-7690. ; 148:24
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Tidskriftsartikel (refereegranskat)abstract
- Unraveling the atomistic details of solid/liquid interfaces, e.g., by means of vibrational spectroscopy, is of vital importance in numerous applications, from electrochemistry to heterogeneous catalysis. Water-oxide interfaces represent a formidable challenge because a large variety of molecular and dissociated water species are present at the surface. Here, we present a comprehensive theoretical analysis of the anharmonic OH stretching vibrations at the water/ZnO(10 (1) over bar0) interface as a prototypical case. Molecular dynamics simulations employing a reactive high-dimensional neural network potential based on density functional theory calculations have been used to sample the interfacial structures. In the second step, one-dimensional potential energy curves have been generated for a large number of configurations to solve the nuclear Schrodinger equation. We find that (i) the ZnO surface gives rise to OH frequency shifts up to a distance of about 4 angstrom from the surface; (ii) the spectrum contains a number of overlapping signals arising from different chemical species, with the frequencies decreasing in the order v (adsorbed hydroxide) > v (non-adsorbed water) > v (surface hydroxide) > v (adsorbed water); (iii) stretching frequencies are strongly influenced by the hydrogen bond pattern of these interfacial species. Finally, we have been able to identify substantial correlations between the stretching frequencies and hydrogen bond lengths for all species.
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