Stability Study of Four Layer Aurivillius Oxide of AxBi4-xTi4O15 (A = Ca, Sr, Ba): Atomistic Simulation

Aurivillius is bismuth layered structure ferroelectrics that can be applied as memory, sensor, and catalyst. This research aimed to study the stability of AxBi4-xTi4O15 Aurivillius (A = Ca, Sr, and Ba). Dopants (A) partially substitute Bi at the sites of Bi(1) and Bi(2) of the perovskite layer. This research method is an atomistic simulation using by the GULP code. Simulations were carried out by means of AxBi4-xTi4O15 geometry optimization at constant pressure, using the Buckingham potential. The results showed that the increase in the concentration of dopants substituting Bi accompanied by an increase in lattice energies. The most stable Aurivillius was CaxBi4-xTi4O15 (x = 16.3%) carried out by Bi substitution at Bi(2) site, with lattice energy, -1668.227 eV. Aurivillius stability decreases by increasing the size of the dopant. The maximum concentration number of A dopant substituting Bi was discussed.

Phase-Transferable Force Field for Alkali Halides

A longstanding goal of computational chemistry is to predict the state of materials in all phases with a single model. This is particularly relevant for materials that are difficult or dangerous to handle or compounds that have not yet been created. Progress towards this goal has been limited as most work has concentrated on just one phase, often determined by particular applications. In the framework of the development of the Alexandria force field we present here new polarizable force fields for alkali halides with Gaussian charge distributions for molecular dynamics simulations. We explore different descriptions of the Van der Waals interaction, like the commonly applied 12-6 Lennard-Jones (LJ), and compare it to \softer" ones, such as 8-6 LJ, Buckingham and a modified Buckingham potential. Our results for physico-chemical properties of the gas, liquid and solid phase of alkali halides, are compared to experimental data and calculations with reference polarizable and non-polarizable force fields. The new polarizable force field that employs a modified Buckingham potential predicts the tested properties for gas, liquid and solid phases with a very good accuracy. In contrast to reference force fields, this model reproduces the correct crystal structures for all alkali halides at low and high temperature. Seeing that experiments with molten salts may be tedious due to high temperatures and their corrosive nature, the models presented here can contribute significantly to our understanding of alkali halides in general and melts in particular.<br>

Phase-Transferable Force Field for Alkali Halides

A longstanding goal of computational chemistry is to predict the state of materials in all phases with a single model. This is particularly relevant for materials that are difficult or dangerous to handle or compounds that have not yet been created. Progress towards this goal has been limited as most work has concentrated on just one phase, often determined by particular applications. In the framework of the development of the Alexandria force field we present here new polarizable force fields for alkali halides with Gaussian charge distributions for molecular dynamics simulations. We explore different descriptions of the Van der Waals interaction, like the commonly applied 12-6 Lennard-Jones (LJ), and compare it to \softer" ones, such as 8-6 LJ, Buckingham and a modified Buckingham potential. Our results for physico-chemical properties of the gas, liquid and solid phase of alkali halides, are compared to experimental data and calculations with reference polarizable and non-polarizable force fields. The new polarizable force field that employs a modified Buckingham potential predicts the tested properties for gas, liquid and solid phases with a very good accuracy. In contrast to reference force fields, this model reproduces the correct crystal structures for all alkali halides at low and high temperature. Seeing that experiments with molten salts may be tedious due to high temperatures and their corrosive nature, the models presented here can contribute significantly to our understanding of alkali halides in general and melts in particular.<br>

An Assessment of Interatomic Potentials for Yittria-Stablized Zirconia

Six interatomic potentials based on Buckingham potential form for yttria-stablized zirconia have been critically assessed by predicting lattice constants, dielectric constants, and elastic properties using the mean-field approach. The content of Y2O3is set to the range from 8 to 24 mol%. It has been found out that no potential can reproduce all the fundamental properties. Taking all the simulation and comparison results into consideration, the potential of Butler (1981) displays the highest fidelity, and the potential of Lewis (1985) shows the widest range of applicability.

STUDY OF IONIC CONDUCTIVITY IN CUBIC CERIA BY THE STATISTICAL MOMENT METHOD

We have investigated the diffusion and ionic conductivity of the cubic ceria CeO 2 using the statistical moment method (SMM) in the statistical physics. The activation energy, diffusion coefficient, pre-exponential factor and ionic conductivity are derived in closed analytic forms. The SMM calculations are performed by using the Buckingham potential for the cubic ceria. The effects of the three different potential parameter sets of the Buckingham potential and influence of dipole polarization effects on activation energy, diffusion coefficient and ionic conductivity for CeO 2 are also investigated. The present analytical formulas including the anharmonic effects of the lattice vibrations give the predicted values of these quantities, which are comparable to those of the experimental values.

Relationship and discrepancies between the Extended-Rydberg and the Generalized Buckingham potential energy functions

This paper relates the interatomic energy according to the Extended-Rydberg and the Generalized Buckingham potential functions by applying a Maclaurin series expansion on the latter and thereafter comparing it with the former. In so doing, the plotted curves of these two functions not only show equal curvature at the equilibrium state, but also reveal a discrepancy for the finite distortion. It is shown that, when equated at equilibrium, the Generalized Buckingham gives a lower energy in comparison to the Extended-Rydberg at finite bond compression and stretching. However, the energy difference diminishes when the interatomic distance exceeds twice that at equilibrium. Due to such discrepancies upon comparative normalization, it would be beneficial for computational chemists to select the appropriate potential function for the purpose of conservative molecular modeling. .

Atomistic Simulation of Displacement Cascades in Zircon

ABSTRACTLow-energy displacement cascades in zircon (ZrSiO4) initiated by a Zr primary knock-on atom have been investigated by molecular dynamics (MD) simulations using a Coulombic model for long-range interactions, Buckingham potential for short-range interactions and Ziegler-Biersack potentials for close pair interactions. Displacements are found to occur mainly in the O sublattice, and O replacements by a ring mechanism are predominant. Clusters containing Si interstitials bridged by O interstitials, vacancy clusters and anti-site defects are found to occur. This Si-O-Si bridging is considerable in ZrSiO4 quenched from the melt in MD simulations.