Interplay of force constants in the lattice dynamics of disordered alloys : An ab-initio study

TL;DR

This study introduces a DFT-based method combining SQS and ASR to accurately predict interatomic force constants and phonon properties in disordered alloys, addressing challenges posed by multisite correlations and atomic size differences.

Contribution

The paper presents a novel systematic approach integrating SQS and ASR within DFT to predict force constants in disordered alloys, validated on TaW and NiPt systems.

Findings

Ta-Ta bond distance is smaller in alloy, leading to stiffer force constants.

Pt-Pt force constants are softer due to larger bond distances.

Results agree with experimental data, confirming the method's reliability.

Abstract

A reliable prediction of interatomic force constants in disordered alloys is an outstanding problem. This is due to the need for a proper treatment of multisite (atleast pair) correlation within a random environment. The situation becomes even more challenging for systems with large difference in atomic size and mass. We propose a systematic density functional theory (DFT) based study to predict the ab-initio force constants in random alloys. The method is based on a marriage between special quasirandom structures (SQS) and the augmented space recursion (ASR) to calculate phonon spectra, density of states (DOS) etc. bcc TaW and fcc NiPt alloys are considered as the two distinct test cases. Ta-Ta (W-W) bond distance in the alloy is predicted to be smaller (larger) than those in pure Ta (W), which, in turn, yields stiffer (softer) force constants for Ta (W). Pt-Pt force constants in the alloy, however, are predicted to be softer compared to Ni-Ni, due to a large bond distance of the former. Our calculated force constants, phonon spectra and DOS are compared with experiments and other theoretical results, wherever available. Correct trend of present results for the two alloys pave a path for further future studies in more complex alloy systems.