Local Volume Effects in the Generalized Pseudopotential Theory

TL;DR

This paper introduces the adaptive GPT (aGPT), an extension of the generalized pseudopotential theory that accounts for local volume effects, enabling accurate simulations of defects and elastic properties in metals.

Contribution

The paper develops a formalism for aGPT that explicitly calculates forces and stress, improving defect and elastic property modeling in metals over traditional GPT.

Findings

Accurate vacancy formation energies in hcp Mg.

Refined elastic constants and phonon dispersion calculations.

Successful implementation of aGPT in molecular dynamics and statics.

Abstract

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. Whilst 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 [PhysRevLett.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 and molecular statics. We apply the aGPT to vacancy formation and divacancy binding in hcp Mg and 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.