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9 results on '"Kattirtzi, John A."'

1. Local distortions and dynamics in hydrated Y-doped BaZrO$_3$

Author

Torayev, Amangeldi, Sperrin, Luke, Gomez, Maria A., Kattirtzi, John A., Merlet, Céline, and Grey, Clare P.

Subjects
Condensed Matter - Materials Science
Abstract

Y-doped BaZrO$_3$ is a promising proton conductor for intermediate temperature solid oxide fuel cells. In this work, a combination of static DFT calculations and DFT based molecular dynamics (DFT-MD) was used to study proton conduction in such a material. Geometry optimisations of 100 structures with a 12.5% dopant concentration allowed us to identify a clear correlation between the bending of the metal-oxygen-metal angle and the energies of the simulated cells. Depending on the type of bending, two configurations, designated as inwards bending and outwards bending, were defined. The results demonstrate that a larger bending decreases the energy and that the lowest energies are observed for structures combining inwards bending with protons being close to the dopant atoms. These lowest energy structures are the ones with the strongest hydrogen bonds. DFT-MD simulations in cells with different yttrium distributions provide complementary microscopic information on proton diffusion as they capture the dynamic distortions of the lattice caused by thermal motion. A careful analysis of the proton jumps between different environments confirmed that the inwards and outwards bending states are relevant for the understanding of proton diffusion. Indeed, intra-octahedral jumps were shown to only occur starting from an outwards configuration while the inwards configuration seems to favor rotations around the oxygen. On average, in the DFT-MD simulations, the hydrogen bond lengths are shorter for the outwards configuration which facilitates the intraoctahedral jumps. Diffusion coefficients and activation energies were also determined and compared to previous theoretical and experimental data showing a good agreement with previous data corresponding to local proton motion., Comment: Preprint

Published
2020
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2. Microscopic dynamics of charge separation at the aqueous electrochemical interface

Author

Kattirtzi, John A., Limmer, David T., and Willard, Adam P.

Subjects
Physics - Chemical Physics, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Statistical Mechanics
Abstract

We have used molecular simulation and methods of importance sampling to study the thermodynamics and kinetics of ionic charge separation at a liquid water-metal interface. We have considered this process using canonical examples of two different classes of ions: a simple alkali-halide pair, Na$^+$I$^-$, or classical ions, and the products of water autoionization, H$_3$O$^+$OH$^-$, or water ions. We find that for both ion classes, the microscopic mechanism of charge separation, including water's collective role in the process, is conserved between the bulk liquid and the electrode interface. Despite this, the thermodynamic and kinetic details of the process differ between these two environments in a way that depends on ion type. In the case of the classical ion pairs, a higher free energy barrier to charge separation and a smaller flux over that barrier at the interface, results in a rate of dissociation that is 40x slower relative to the bulk. For water ions, a slightly higher free energy barrier is offset by a higher flux over the barrier from longer lived hydrogen bonding patters at the interface, resulting in a rate of association that is similar both at and away from the interface. We find that these differences in rates and stabilities of charge separation are due to the altered ability of water to solvate and reorganize in the vicinity of the metal interface., Comment: 6 pages, 3 figures + SI

Published
2017
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3. Microscopic dynamics of charge separation at the aqueous electrochemical interface

Author

Kattirtzi, John A, Limmer, David T, and Willard, Adam P

Subjects
Chemical Sciences, Physical Chemistry, Affordable and Clean Energy, chemical kinetics, catalysis, surface science, ion pairing
Abstract

We have used molecular simulation and methods of importance sampling to study the thermodynamics and kinetics of ionic charge separation at a liquid water-metal interface. We have considered this process using canonical examples of two different classes of ions: a simple alkali-halide pair, Na+I-, or classical ions, and the products of water autoionization, H3O+OH-, or water ions. We find that for both ion classes, the microscopic mechanism of charge separation, including water's collective role in the process, is conserved between the bulk liquid and the electrode interface. However, the thermodynamic and kinetic details of the process differ between these two environments in a way that depends on ion type. In the case of the classical ion pairs, a higher free-energy barrier to charge separation and a smaller flux over that barrier at the interface result in a rate of dissociation that is 40 times slower relative to the bulk. For water ions, a slightly higher free-energy barrier is offset by a higher flux over the barrier from longer lived hydrogen-bonding patterns at the interface, resulting in a rate of association that is similar both at and away from the interface. We find that these differences in rates and stabilities of charge separation are due to the altered ability of water to solvate and reorganize in the vicinity of the metal interface.

Published
2017

5. Towards an atomistic understanding of disordered carbon electrode materials

Author

Deringer, Volker L., Merlet, Céline, Hu, Yuchen, Lee, Tae Hoon, Kattirtzi, John A., Pecher, Oliver, Csányi, Gábor, Elliott, Stephen R., Grey, Clare P., University of Cambridge [UK] (CAM), Centre interuniversitaire de recherche et d'ingenierie des matériaux (CIRIMAT), Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Institut de Chimie du CNRS (INC), Réseau sur le stockage électrochimique de l'énergie (RS2E), Université de Picardie Jules Verne (UPJV)-Institut de Chimie du CNRS (INC)-Aix Marseille Université (AMU)-Université de Pau et des Pays de l'Adour (UPPA)-Université de Nantes (UN)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Collège de France (CdF (institution))-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA)-Université Grenoble Alpes (UGA)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM), Xiamen University, Centre National de la Recherche Scientifique - CNRS (FRANCE), Collège de France (FRANCE), Ecole Nationale Supérieure de Chimie de Paris - ENSCP (FRANCE), Ecole Nationale Supérieure de Chimie de Montpellier - ENSCM (FRANCE), Institut National Polytechnique de Toulouse - INPT (FRANCE), Institut polytechnique de Grenoble (FRANCE), NMR Service GmbH (GERMANY), Sorbonne Université (FRANCE), University of Cambridge (UNITED KINGDOM), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), Université de Nantes (FRANCE), Université de Picardie Jules Verne (FRANCE), Xiamen University (CHINA), Université de Pau et des Pays de l'Adour - UPPA (FRANCE), Université de Haute Alsace - UHA (FRANCE), Université de Montpellier (FRANCE), Centre Interuniversitaire de Recherche et d'Ingénierie des Matériaux - CIRIMAT (Toulouse, France), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT), Université de Nantes (UN)-Aix Marseille Université (AMU)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Collège de France (CdF (institution))-Université de Picardie Jules Verne (UPJV)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Pau et des Pays de l'Adour (UPPA)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA)-Université Grenoble Alpes (UGA), Deringer, Volker [0000-0001-6873-0278], Merlet, Celine [0000-0003-3758-273X], Grey, Clare [0000-0001-5572-192X], Apollo - University of Cambridge Repository, and Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)

Subjects
0306 Physical Chemistry (incl. Structural), inorganic chemicals, [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry, Energie électrique, [INFO.INFO-LG]Computer Science [cs]/Machine Learning [cs.LG], Matériaux, Carbon electrode materials, [CHIM.MATE]Chemical Sciences/Material chemistry, 0912 Materials Engineering
Abstract

International audience; Disordered nanoporous and ''hard'' carbons are widely used in batteries and supercapacitors, but their atomic structures are poorly determined. Here, we combine machine learning and DFT to obtain new atomistic insight into carbonaceous energy materials. We study structural models of porous and graphitic carbons, and Na intercalation as relevant for sodium-ion batteries.

Published
2018

6. Microscopic dynamics of charge separation at the aqueous electrochemical interface

Author

Massachusetts Institute of Technology. Department of Chemistry, Kattirtzi, John A, Limmer, David T., Willard, Adam P., Massachusetts Institute of Technology. Department of Chemistry, Kattirtzi, John A, Limmer, David T., and Willard, Adam P.

Abstract

Aqueous electrode interfaces serve as the backdrop for many important chemical processes in nature and technology. These interfaces continually garner much interest due to their ability to facilitate and even catalyze certain electrochemical reactions. Charge separation is a fundamental step in nearly all catalytic processes that occur at metal interfaces. Traditional electrochemical measurements are able to observe the consequences of charge separation but are limited in their ability to reveal direct molecular details. By studying detailed molecular models of charge transfer at water metal interfaces, we have uncovered the microscopic dynamics of this fundamental process. Elucidating the altered thermodynamics and kinetics of charge separation at water–metal interfaces and identifying their molecular underpinnings will inform the interpretation of macroscopic measurements and the design of better catalysts., Massachusetts Institute of Technology. Department of Chemistry

Published
2018

7. Microscopic dynamics of charge separation at the aqueous electrochemical interface.

Author

Willard, Adam P., Kattirtzi, John A., and Limmer, David T.

Subjects
*ELECTROCHEMICAL analysis, *MOLECULAR dynamics, *THERMODYNAMICS, *AUGER effect, *CHEMICAL reactions
Abstract

We have used molecular simulation and methods of importance sampling to study the thermodynamics and kinetics of ionic charge separation at a liquid water-metal interface. We have considered this process using canonical examples of two different classes of ions: a simple alkali-halide pair, Na+I-, or classical ions and the products of water autoionization, H3O+OH-, or water ions. We find that for both ion classes, the microscopic mechanism of charge separation, including water's collective role in the process, is conserved between the bulk liquid and the electrode interface. However, the thermodynamic and kinetic details of the process differ between these two environments in a way that depends on ion type. In the case of the classical ion pairs, a higher free-energy barrier to charge separation and a smaller flux over that barrier at the interface result in a rate of dissociation that is 40 times slower relative to the bulk. For water ions, a slightly higher free-energy barrier is offset by a higher flux over the barrier from longer lived hydrogen-bonding patterns at the interface, resulting in a rate of association that is similar both at and away from the interface.We find that these differences in rates and stabilities of charge separation are due to the altered ability of water to solvate and reorganize in the vicinity of the metal interface. [ABSTRACT FROM AUTHOR]

Published
2017
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8. Shielding Constants and Chemical Shifts in DFT: Influence of Optimized Effective Potential and Coulomb-Attenuation

Author

Peach, Michael J. G., Kattirtzi, John A., Teale, Andrew M., Tozer, David J., Peach, Michael J. G., Kattirtzi, John A., Teale, Andrew M., and Tozer, David J.

Abstract

The influence of the optimized effective potential (OEP) and Coulomb-attenuation on shielding constants and chemical shifts is investigated for three disparate categories of molecule: main group, hydrogen bonded, and transition metal systems. Expanding the OEP in the orbital basis leads to physically sensible exchange-correlation potentials; OEP generalized gradient approximation results provide some indication of the accuracy of the expansion. OEP uncoupled magnetic parameters from representative hybrid and Coulomb-attenuated functionals can be a dramatic improvement over conventional results; both categories yield similar accuracy. Additional flexibility is introduced by expanding the OEP in an extensive even-tempered basis set, but this leads to the well-known problem of unphysical, oscillatory potentials. Smooth potentials are recovered through the use of a smoothing norm, but deficiencies in the procedure are highlighted for transition metal complexes. The study reiterates the importance of the OEP procedure in magnetic response calculations using orbital-dependent functionals, together with the need for careful attention to ensure physically sensible potentials. It also illustrates the utility of Coulomb-attenuated functionals for computing short-range molecular properties.

Published
2010

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