Ab initio study of InxGa(1-x)N - performance of the alchemical mixing approximation

TL;DR

This study uses the ab initio alchemical mixing approximation within the ABINIT package to analyze structural, elastic, and electronic properties of InxGa(1-x)N alloys, providing new composition-dependent elastic data and assessing the method's accuracy.

Contribution

It introduces and evaluates the alchemical mixing approximation for InxGa(1-x)N alloys, including new composition-dependent elastic constants and pressure derivatives, compared to existing supercell calculations.

Findings

Elastic constants vary with composition in ZB structures.

New data on pressure derivatives of elastic constants.

Assessment of the alchemical mixing approximation's performance.

Abstract

The alchemical mixing approximation which is the ab initio pseudopotential specific implementation of the virtual crystal approximation (VCA), offered in the ABINIT package, has been employed to study the wurtzite (WZ) and zinc blende (ZB) InxGa(1-x)N alloy from first principles. The investigations were focused on structural properties (the equilibrium geometries), elastic properties (elastic constants and their pressure derivatives), and on the band-gap. Owing to the ABINIT functionality of calculating the Hellmann-Feynmann stresses, the elastic constants have been evaluated directly from the strain-stress relation. Values of all the quantities calculated for parent InN and GaN have been compared with the literature data and then evaluated as functions of composition x on a dense, 0.05 step, grid. Some results have been obtained which, to authors' knowledge, have not yet been reported in the literature, like composition dependent elastic constants in ZB structures or composition dependent pressure derivatives of elastic constants. The band-gap has been calculated within the MBJLDA approximation. Additionally, the band-gaps for pure $InN$ and GaN have been calculated with the Wien2k code, for comparison purposes. The evaluated quantities have been compared with the available literature reporting supercell-based ab initio calculations and on that basis conclusions concerning the performance of the alchemical mixing approach have been drawn. ...