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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenSat, 13 Apr 2024 02:13:23 +0000The ReaxFF polarizable reactive force fields for molecular dynamics simulation of ferroelectrics
https://resolver.caltech.edu/CaltechAUTHORS:20111026-130045474
Authors: {'items': [{'id': 'Goddard-W-A-III', 'name': {'family': 'Goddard', 'given': 'William A., III'}, 'orcid': '0000-0003-0097-5716'}, {'id': 'Zhang-Qingsong', 'name': {'family': 'Zhang', 'given': 'Qingsong'}}, {'id': 'Uludoğan-Mustafa', 'name': {'family': 'Uludoğan', 'given': 'Mustafa'}}, {'id': 'Strachan-Alejandro', 'name': {'family': 'Strachan', 'given': 'Alejandro'}, 'orcid': '0000-0002-4174-9750'}, {'id': 'Çağin-T', 'name': {'family': 'Çağin', 'given': 'Tahir'}, 'orcid': '0000-0002-3665-0932'}]}
Year: 2002
DOI: 10.1063/1.1499551
We use ab initio Quantum Mechanical (QM) calculations to derive a force field that accurately describes the atomic interactions in BaTiO3 allowing, via Molecular Dynamics (MD), the simulation of thousands of atoms. A key feature of the force field (denoted ReaxFF) is that charge transfer and atomic polarization are treated self-consistently. The charge on each atom is separated into a core, described as a Gaussian distribution with fixed total charge (e.g. +4 for Ti), and a valence charge, also described as a Gaussian distribution. The valence charges can flow in response to its environment as described via Charge Equilibration (QEq). The restoring force between a core and its valence electrons is given be the electrostatic interaction between the two charge distributions. Thus each atom has four universal parameters describing the electrostatics which are determined once from fitting to the QM charge distributions on a representative set of finite clusters. The nonelectrostatic interactions (Pauli repulsion, dispersion) are described with a Morse potential, leading to 3 additional universal parameters for each pair of atoms. We optimized the Morse parameters to reproduce the zero temperature Equation of State (energy- and pressure-volume curves) obtained using QM methods of cubic and tetragonal BaTiO_3 over a wide pressure range. We then use the ReaxFF with MD to study thermal properties of BaTiO_3, in particular the cubic to tetragonal phase transition. Our MD simulations indicate that the transition temperature obtained using ReaxFF is in good agreement with experiment.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/620xv-s7b62ReaxFF_(SiO) Reactive Force Field for Silicon and Silicon Oxide Systems
https://resolver.caltech.edu/CaltechAUTHORS:20170630-130928587
Authors: {'items': [{'id': 'van-Duin-A-C-T', 'name': {'family': 'van Duin', 'given': 'Adri C. T.'}, 'orcid': '0000-0002-3478-4945'}, {'id': 'Strachan-Alejandro', 'name': {'family': 'Strachan', 'given': 'Alejandro'}, 'orcid': '0000-0002-4174-9750'}, {'id': 'Stewman-Shannon', 'name': {'family': 'Stewman', 'given': 'Shannon'}}, {'id': 'Zhang-Qingsong', 'name': {'family': 'Zhang', 'given': 'Qingsong'}}, {'id': 'Xu-Xin', 'name': {'family': 'Xu', 'given': 'Xin'}}, {'id': 'Goddard-W-A-III', 'name': {'family': 'Goddard', 'given': 'William A., III'}, 'orcid': '0000-0003-0097-5716'}]}
Year: 2003
DOI: 10.1021/jp0276303
To predict the structures, properties, and chemistry of materials involving silicon and silicon oxides; interfaces between these materials; and hydrolysis of such systems, we have developed the ReaxFF_(SiO), reactive force field. The parameters for this force field were obtained from fitting to the results of quantum chemical (QC) calculations on the structures and energy barriers for a number of silicon oxide clusters and on the equations of state for condensed phases of Si and SiO_2 from QC. We expect that ReaxFF_(SiO) will allow accurate dynamical simulations of bond breaking processes in large silicon and silicon oxide systems. ReaxFF_(SiO) is based closely on the potential functions of the ReaxFF_(CH) reactive force field for hydrocarbons, so that it should also be useful for describing reactions of organics with Si and SiO_2 systems.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zw0kz-frc52An extended hybrid density functional (X3LYP) with improved descriptions of nonbond interactions and thermodynamic properties of molecular systems
https://resolver.caltech.edu/CaltechAUTHORS:XUXjcp05
Authors: {'items': [{'id': 'Xu-Xin', 'name': {'family': 'Xu', 'given': 'Xin'}}, {'id': 'Zhang-Qingsong', 'name': {'family': 'Zhang', 'given': 'Qingsong'}}, {'id': 'Muller-R-P', 'name': {'family': 'Muller', 'given': 'Richard P.'}}, {'id': 'Goddard-W-A-III', 'name': {'family': 'Goddard', 'given': 'William A., III'}, 'orcid': '0000-0003-0097-5716'}]}
Year: 2005
DOI: 10.1063/1.1812257
We derive here the form for the exact exchange energy density for a density that decays with Gaussian-type behavior at long range. This functional is intermediate between the B88 and the PW91 exchange functionals. Using this modified functional to match the form expected for Gaussian densities, we propose the X3LYP extended functional. We find that X3LYP significantly outperforms Becke three parameter Lee–Yang–Parr (B3LYP) for describing van der Waals and hydrogen bond interactions, while performing slightly better than B3LYP for predicting heats of formation, ionization potentials, electron affinities, proton affinities, and total atomic energies as validated with the extended G2 set of atoms and molecules. Thus X3LYP greatly enlarges the field of applications for density functional theory. In particular the success of X3LYP in describing the water dimer (with Re and De within the error bars of the most accurate determinations) makes it an excellent candidate for predicting accurate ligand–protein and ligand–DNA interactions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fhsxn-1kc75The ferroelectric and cubic phases in BaTiO_3 ferroelectrics are also antiferroelectric
https://resolver.caltech.edu/CaltechAUTHORS:ZHApnas06
Authors: {'items': [{'id': 'Zhang-Qingsong', 'name': {'family': 'Zhang', 'given': 'Qingsong'}}, {'id': 'Çağin-T', 'name': {'family': 'Çağin', 'given': 'Tahir'}, 'orcid': '0000-0002-3665-0932'}, {'id': 'Goddard-W-A-III', 'name': {'family': 'Goddard', 'given': 'William A., III'}, 'orcid': '0000-0003-0097-5716'}]}
Year: 2006
DOI: 10.1073/pnas.0606612103
PMCID: PMC1595414
Using quantum mechanics (QM, Density Functional Theory) we show that all four phases of barium titanate (BaTiO3) have local Ti distortions toward <111> (an octahedral face). The stable rhombohedral phase has all distortions in phase (ferroelectric, FE), whereas higher temperature phases have antiferroelectric coupling (AFE) in one, two, or three dimensions (orthorhombic, tetragonal, cubic). This FE–AFE model from QM explains such puzzling aspects of these systems as the allowed Raman excitation observed for the cubic phase, the distortions toward <111> observed in the cubic phase using x-ray fine structure, the small transition entropies, the heavily damped soft phonon modes, and the strong diffuse x-ray scattering in all but the rhombohedral phase. In addition, we expect to see additional weak Bragg peaks at the face centers of the reciprocal lattice for the cubic phase. Similar FE–AFE descriptions are expected to occur for other FE materials. Accounting for this FE–AFE nature of these phases is expected to be important in accurately simulating the domain wall structures, energetics, and dynamics, which in turn may lead to the design of improved materials.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/31qfn-d9167Charge and polarization distributions at the 90° domain wall in barium titanate ferroelectric
https://resolver.caltech.edu/CaltechAUTHORS:ZHAapl06b
Authors: {'items': [{'id': 'Zhang-Qingsong', 'name': {'family': 'Zhang', 'given': 'Qingsong'}}, {'id': 'Goddard-W-A-III', 'name': {'family': 'Goddard', 'given': 'William A., III'}, 'orcid': '0000-0003-0097-5716'}]}
Year: 2006
DOI: 10.1063/1.2374676
The authors use the PQEq force field based on quantum mechanics studies to provide a first-principles description of the 90° domain wall in barium titanate. Using periodic cells with lengths of up to 74 nm (5120 atoms), the authors find that the domain wall thickness is 21 nm in which the polarization switches over a 5 nm central layer surrounded by two transition layers each 8 nm wide. The central 5 nm layer consists of a 2 nm sublayer with overshooting polarizations and a 3 nm sublayer with reversed polarization. This structure explains the discrepancies in previous analyses, which have suggested domain walls ranging from 100 nm to 1 nm. These results should be of particular importance in developing nanoscale ferroelectric devices.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ytvv9-7qm27