Calculating the Stability of Different Surfaces of GaAsxP1-x Mixed-Crystals using the Virtual Crystal Approximation

TL;DR

This paper compares super cell and Virtual Crystal Approximation methods for calculating the stability of GaAsxP1-x surfaces, highlighting VCA's strengths and limitations in modeling mixed-crystals.

Contribution

It demonstrates the application of VCA to surface stability analysis of mixed-crystals and compares its performance with super cell methods.

Findings

VCA overestimates total energy but models density of states well

Bulk crystal has minor influence on surface configuration

VCA is a useful but imperfect tool for surface stability calculations

Abstract

The theoretical treatment of mixed-crystals is very demanding. A straight-forward approach to attack this problem is using a super cell method (SCM). Another one is the Virtual Crystal Approximation (VCA), which is a feature of the Vienna Ab initio Simulation Package (VASP). For comparison we use both methods to calculate the total energy (Etot) and the density of states (DOS) of bulk GaAsxP1-x. We then apply VCA to compute the stability of different surfaces using an extended version of the surface formation energy Omega. Our calculations show, on one hand, a working VCA implementation with its flaws (overestimation of Etot) and strengths (well modelling of DOS). On other hand, a further result is that bulk of the slab of a mixed-crystal has a minor influence on the configuration of the surface.