Linearized force constants method for lattice dynamics in mixed semiconductors

TL;DR

The paper introduces a simple, accurate linearized method for calculating phonon spectra in mixed semiconductors based on first-principles data, effectively reproducing ab initio results for alloy systems.

Contribution

It proposes a novel linearized force constants approach that simplifies phonon calculations in mixed semiconductors using bond-length dependent force constants.

Findings

Accurately reproduces phonon spectra compared to ab initio calculations.

Effective for different alloy compositions in tested systems.

Simplifies computational process for lattice dynamics.

Abstract

A simple and accurate method of calculating phonon spectra in mixed semiconductors alloys, on the basis of preliminarily (from first principles) relaxed atomic structure, is proposed and tested for (Zn,Be)Se and (Ga,In)As solid solutions. The method uses an observation that the interatomic force constants, calculated ab initio for a number of microscopic configurations in the systems cited, show a clear linear variation of the main (diagonal) values of the interatomic force constants with the corresponding bond length. We formulate simple rules about how to recover the individual 3x3 subblocks of the force constants matrix in their local (bonds-related) coordinate systems and how to transform them into a global (crystal cell-related) coordinate system. Test calculations done for 64-atom supercells representing different concentrations of (Zn,Be)Se and (Ga,In)As show that the phonon frequencies and compositions of eigenvectors are faithfully reproduced in a linearized force constants calculation, as compared to true ab initio calculations.