Local volume effects in the generalized pseudopotential theory
GCG Skinner and AT Paxton and JA Moriarty, PHYSICAL REVIEW B, 99, 214107 (2019).
The generalized pseudopotential theory (GPT) is a powerful method for deriving real-space transferable interatomic potentials. Using a coarse- grained electronic structure, one can explicitly calculate the pair ion- ion and multi-ion interactions in simple and transition metals. While successful in determining bulk properties, in central force metals the GPT fails to describe crystal defects for which there is a significant local volume change. A previous paper J. A. Moriarty and R. Phillips, Phys. Rev. Lett. 66, 3036 (1991) found that by allowing the GPT total energy to depend upon some spatially averaged local electron density, the energetics of vacancies and surfaces could be calculated within experimental ranges. In this paper, we develop the formalism further by explicitly calculating the forces and stress tensor associated with this total energy. We call this scheme the adaptive GPT (aGPT) and it is capable of both molecular dynamics (MD) and molecular statics. We apply the aGPT to vacancy formation, divacancy binding, and stacking faults in hcp Mg. We also calculate the local electron density corrections to the bulk elastic constants and phonon dispersion for which there is refinement over the baseline GPT treatment. In addition, we demonstrate aGPT-MD simulation through the calculation of thermal expansion in magnesium to 700 K.
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