(775c) Application of Bond-Valence Theory for Developing Efficient Interatomic Potential for Oxides

First-principles density functional theory (DFT) calculations have played an important role in enhancing microscopic understanding of intrinsic effects (e.g., compositions and structures) on material properties of oxides.[1-2] For elucidating the changes (dynamics) in material behaviors with extrinsic effects, such as temperature, strain, and electric field, large system sizes and long simulations are necessary. Conventional first-principles methods for large systems and long-time simulations are limited due to their intense computational costs. There is therefore still a strong need to develop accurate and efficient atomistic potential that could reproduce the full dynamical behaviors of metal oxides. [3-9] The development of general atomistic potentials for oxides has proven difficult due to the complex nature of various metal-oxygen bonds.[10]

In this work, we developed a bond-valence model based on the principles of bond-valence and bond-valence vector conservation. [11-12] The relationship between the bond-valence model and the bond-order potential is derived analytically in the framework of a tight-binding model, demonstrating that our model is formally equivalent to the bond-order potential, but is dramatically more efficient computationally. A new energy term, bond-valence vector energy, is introduced into the atomistic model. The force fields for PbTiO₃ and BiFeO₃ are parameterized respectively. [13] The new model potential can be applied to both canonical ensemble (NVT) and isobaric-isothermal ensemble (NPT) molecular dynamics (MD) simulations. Our model potential can reproduce the experimental phase transition in NVT MD simulations and also exhibit the experimental sequence of temperature-driven and pressure-driven phase transitions in NPT simulations. We expect that our bond-valence model can be applied to a broad range of inorganic materials.

References

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[13] S. Liu, I. Grinberg, and A. M. Rappe,  J. Phys. Cond. Matt. 25, 102202 (2013)