SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "LAR1:uu ;pers:(Ahuja Rajeev);conttype:(scientificother)"

Sökning: LAR1:uu > Ahuja Rajeev > Övrigt vetenskapligt/konstnärligt

  • Resultat 1-10 av 71
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • Arapan, Sergiu, 1973- (författare)
  • Understanding Physical Reality via Virtual Experiments
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this thesis I have studied some problems of condensed matter at high pressures and temperatures by means of numerical simulations based on Density Functional Theory (DFT).The stability of MgCO3 and CaCO3 carbonates at the Earth's mantle conditions may play an important role in the global carbon cycle through the subduction of the oceanic crust. By performing ab initio electronic structure calculations, we observed a new high-pressure phase transition within the Pmcn structure of CaCO3. This transformation is characterized by the change of the sp-hybridization state of carbon atom and indicates a change to a new crystal-chemical regime. By performing ab initio Molecular Dynamics simulations we show the new phase to be stable at 250 GPa and 1000K. Thus, the formation of sp3 hybridized bonds in carbonates can explain the stability of MaCO3 and CaCO3 at pressures corresponding to the Earth's lower mantle conditions. We have also calculated phase transition sequence in CaCO3, SrCO3 and BaCO3, and have found that, despite the fact that these carbonates are isostructural and undergo the same type of aragonite to post-aragonite transition, their phase transformation sequences are different at high pressures.The continuous improvement of the high-pressure technique led to the discovery of new composite structures at high pressures and complex phases of many elements in the periodic table have been determined as composite host-guest incommensurate structures. We propose a procedure to accurately describe the structural parameters of an incommensurate phase using ab initio methods by approximating it with a set of analogous commensurate supercells and exploiting the fact that the total energy of the system is a function of structural parameters. By applying this method to the Sc-II phase, we have determined the incommensurate ratio, lattice parameters and Wyckoff positions of Sc-II in excellent agreement with the available experimental data. Moreover, we predict the occurrence of an incommensurate high-pressure phase in Ca from first-principle calculations within this approach.The implementation of DFT in modern electronic structure calculation methods proved to be very successful in predicting the physical properties of a solid at low temperature. One can rigorously describe the thermodynamics of a crystal via the collective excitation of the ionic lattice, and the ab initio calculations give an accurate phonon spectra in the quasi-harmonic approximation. Recently an elegant method to calculate phonon spectra at finite temperature in a self-consistent way by using first principles methods has been developed. Within the framework of self-consistent ab initio lattice dynamics approach (SCAILD) it is possible to reproduce the observed stable phonon spectra of high-temperature bcc phase of Ti, Zr and Hf with a good accuracy. We show that this method gives also a good description of the thermodynamics of hcp and bcc phases of Ti, Zr and Hf at high temperatures, and we provide a procedure for the correct estimation of the hcp to bcc phase transition temperature.
  •  
2.
  •  
3.
  • Araújo, Rafael Barros Neves de (författare)
  • Energy Storage Materials: Insights From ab Initio Theory : Diffusion, Structure, Thermodynamics and Design.
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The development of science and technology have provided a lifestyle completely dependent on energy consumption. Devices such as computers and mobile phones are good examples of how our daily life depends on electric energy. In this scenario, energy storage technologies emerge with strategic importance providing efficient ways to transport and commercialize the produced energy. Rechargeable batteries come as the most suitable alternative to fulfill the market demand due to their higher energy- and power- density when compared with other electrochemical energy storage systems. In this context, during the production of this thesis, promising compounds for advanced batteries application were investigated from the theoretical viewpoint. The framework of the density functional theory has been employed together with others theoretical tools to study properties such as ionic diffusion, redox potential, electronic structure and crystal structure prediction.Different organic materials were theoretically characterized with quite distinct objectives. For instance, a protocol able to predict the redox potential in solution of long oligomers were developed and tested against experimental measurements. Strategies such as anchoring of small active molecules on polymers backbone have also been investigated through a screening process that determined the most promising candidates. Methods such as evolutionary simulation and basin-hopping algorithm were employed to search for global minimum crystal structures of small molecules and inorganic compounds working as a cathode of advanced sodium batteries. The crystal structure evolution of C6Cl4O2 upon Na insertion was unveiled and the main reasons behind the lower specific capacity obtained in the experiment were clarified. Ab initio molecular dynamics and the nudged elastic band method were employed to understand the underlying ionic diffusion mechanisms in the recently proposed Alluaudite and Eldfellite cathode materials. Moreover, it was demonstrated that electronic conduction in Na2O2, a byproduct of the Na-O2 battery, occurs via hole polarons hopping. Important physical and chemical insights were obtained during the production of this thesis. It finally supports the development of low production cost, environmental friendliness and efficient electrode compounds for advanced secondary batteries. 
  •  
4.
  •  
5.
  • Banerjee, Amitava (författare)
  • Materials Modelling for Energy Harvesting : From Conversion to Application through Storage
  • 2019
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this Ph.D. thesis, ab initio density functional theory along with molecular dynamics and global optimization methods are used to unveil and understand the structures and properties of energy relevant materials. In this connection, the following applications are considered: i. electrocatalyst for solar fuel production through water splitting, ii. hybrid perovskite solar cell for generation of electrical energy and iii. Battery materials to store the electrical energy. The water splitting mechanism in terms of hydrogen evolution and oxygen evolution reactions (HER and OER) on the catalytic surfaces has been envisaged based on the free energy diagram, named reaction coordinate, of the reaction intermediates. The Ti-functionalized two-dimensional (2D) borophene monolayer has been emerged as a promising material for HER and OER mechanisms as compared to the pristine borophene sheet. Further investigation in the series of this noble metal free monolayer catalyst is 2D Al2C monolayer both in form of pristine and functionalized with nitrogen (N), phosphorous (P), boron (B), and sulphur (S). It has been observed that only B substituted Al2C shows very close to thermoneutral, that could be the most promising candidate for HER on functionalized Al2C monolayer. The adsorption of O* intermediate is stronger in S-substituted Al2C, whereas it is less strongly adsorbed on N-substituted Al2C. The subsequent consideration is being the case of n-type doping (W) along with Ti codoped in BiVO4 to enhance the efficiency of BiVO4 photoanode for water splitting. The determined adsorption energy and corresponding Gibbs free energies depict that the Ti site is energetically more favorable for water splitting. Moreover, the Ti site possesses a lower overpotential in the W–Ti codoped sample as compared to the mono-W doped sample. We have also explored the effect of mixed cation and mixed anion substitution in the hybrid perovskite in terms of structural stability, electronic properties and optical response of hybrid perovskite crystal structures. It has been found that the insertion of bromine (Br) into the system could modulate the stability of the Guanidinium lead iodide (GAPbI3) hybrid perovskite.  Moreover, the band gap of the mixed hybrid perovskite is increased with the inclusion of smaller Br anion while replacing partially the larger iodine (I) anion. Finally the electrochemical storage mechanism for Sodium (Na) and lithium (Li) ion insertion has been envisaged in inorganic electrode (eldfellite, NaFe(SO4)2) as well as in more sustainable organic electrode (di-lithium terephthalate, Li2TP). The full desodiation capability of the eldfellite enhances the capacity while the activation energies (higher than 1 eV) for the Na+ ion diffusion for the charged state lower the ionic insertion rate. The key factor as the variation of Li-O coordination in the terephthalate, for the disproportionation redox reaction in Li2TP is also identified.
  •  
6.
  •  
7.
  • Banerjee, Amitava, et al. (författare)
  • Reaction Coordinate Mapping of Hydrogen Evolution Mechanism on Mg3N2Monolayer
  • 2020
  • Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199 .- 1879-3487.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • In this work, we have envisaged the hydrogen evolution reaction (HER) mechanism on Mg3N2 monolayer based on electronic structure calculations within the framework of density functional theory (DFT) formalism. The semiconducting nature of Mg3N2 monolayer motivates us to investigate the HER mechanism on this sheet. We have constructed the reaction coordinate associated with HER mechanism after determining the hydrogen adsorption energy on Mg3N2 monolayer, while investigating all possible adsorption sites. After obtaining the adsorption energy, we subsequently obtain the adsorption free energy while adding zero point energy difference (Delta ZPE) and entropic contribution (T Delta S). We have not only confined our investigations to a single hydrogen, but have thoroughly observed the adsorption phenomena for increasing number of hydrogen atoms on the surface. We have determined the projected density of states (DOS) in order to find the elemental contribution in the valence band and conduction band regime for all the considered cases. We have also compared the work function value among all the cases, which quantifies the amount of energy required for taking an electron out of the surface. The charge transfer mechanism is also being investigated in order to correlate with the HER mechanism with amount of charge transfer. This is the first attempt on this material to the best of our knowledge, where theoretical investigation has been done to mapping the reaction coordinate of HER mechanism with the associated charge transfer process and the work function values, not only for single hydrogen adsorption, but also for increasing number of adsorbed hydrogen.
  •  
8.
  •  
9.
  • Blomqvist, Andreas (författare)
  • Insights into Materials Properties from Ab Initio Theory : Diffusion, Adsorption, Catalysis & Structure
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this thesis, density functional theory (DFT) calculations and DFT based ab initio molecular dynamics simulations have been employed in order to gain insights into materials properties like diffusion, adsorption, catalysis, and structure. In transition metals, absorbed hydrogen atoms self-trap due to localization of metal d-electrons. The self-trapping state is shown to highly influence hydrogen diffusion in the classical over-barrier jump temperature region. Li diffusion in Li-N-H systems is investigated. The diffusion in Li3N is shown to be controlled by the concentration of vacancies. Exchanging one Li for H (Li2NH), gives a system where the diffusion no longer is dependent on the concentrations of vacancies, but instead on N-H rotations. Furthermore, exchanging another Li for H (LiNH2), results in a blockade of Li diffusion. For high-surface area hydrogen storage materials, metal organic frameworks and covalent organic frameworks, the hydrogen adsorption is studied. In metal organic frameworks, a Li-decoration is also suggested as a way to increase the hydrogen adsorption energy. In NaAlH4 doped with transition metals (TM), the hypothesis of TM-Al intermetallic alloys as the main catalytic species is supported. The source of the catalytic effect of carbon nanostructures on hydrogen desorption from NaAlH4 is shown to be the high electronegativity of the carbon nanostructures. A space-group optimized ab initio random structure search method is used to find a new ground state structure for BeC2 and MgC2. The fast change between the amorphous and the crystalline phase of GeSbTe phase-change materials is suggested to be due to the close resemblance between the local amorphous structure and the crystalline structure. Finally, we show that more than 80% of the voltage in the lead acid battery is due to relativistic effects.  
  •  
10.
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-10 av 71
Typ av publikation
annan publikation (32)
doktorsavhandling (28)
tidskriftsartikel (7)
konferensbidrag (3)
konstnärligt arbete (2)
licentiatavhandling (1)
visa fler...
visa färre...
Typ av innehåll
Författare/redaktör
Grigoriev, Anton (15)
Ahuja, Rajeev, 1965- (14)
Ahuja, Rajeev, Profe ... (9)
Chakraborty, Sudip (8)
Ramzan, Muhammad, 19 ... (7)
visa fler...
Banerjee, Amitava (6)
Ottosson, Henrik (6)
Johansson, Börje (4)
Blomqvist, Andreas (4)
Leifer, Klaus (4)
Scheicher, Ralph H. (4)
Löfås, Henrik (4)
Johansson, Robert (3)
Luo, Wei (3)
Eriksson, Olle (3)
Panda, Pritam Kumar, ... (3)
Ahuja, Rajeev, Profe ... (3)
Löfås, Henrik, 1983- (3)
Shukla, Vivekanand (3)
Ahuja, Rajeev, Prof. (3)
Rensmo, Håkan (2)
Boschloo, Gerrit (2)
Schmitt, Thorsten (2)
Mattesini, Maurizio (2)
Johansson, Erik M. J ... (2)
Orthaber, Andreas, 1 ... (2)
Leifer, Klaus, 1965- (2)
Naqvi, S. Rabab (2)
Guo, Jinghua (2)
Muscas, Giuseppe (2)
Dong, Chungli (2)
Duda, Laurent-C. (2)
Barros Neves de Arau ... (2)
Blom, Tobias (2)
Jafri, S. Hassan. M. (2)
Wani, Ishtiaq Hassan ... (2)
Hayat, Aqib (2)
Jönsson, Petra (2)
Prasongkit, Jariyane ... (2)
Edin, Emil (2)
Isberg, Jan, Prof. (2)
Wallner, Andreas (2)
Jafri, Syed Hassan M ... (2)
Scheicher, Ralph (2)
Kaewmaraya, Thanayut (2)
Cameau, Mathis (2)
Zhu, Huimin (2)
Kaewmaraya, Thanayut ... (2)
Saini, Naurang (2)
visa färre...
Lärosäte
Uppsala universitet (71)
Kungliga Tekniska Högskolan (2)
Språk
Engelska (71)
Forskningsämne (UKÄ/SCB)
Naturvetenskap (53)
Teknik (6)
Medicin och hälsovetenskap (1)

År

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy