High pressure and temperature thermoelasticity of hcp osmium from ab initio quasi-harmonic theory

TL;DR

This study uses ab initio quasi-harmonic theory to accurately analyze the thermoelastic properties of hcp osmium across various temperatures and pressures, validating approximations and comparing with experimental data.

Contribution

It provides a comprehensive assessment of the thermoelastic properties of osmium using QHA, validating the ZSISA and V-ZSISA approximations against full free energy minimization.

Findings

ZSISA and V-ZSISA approximations are highly accurate for osmium.

QHA-derived elastic constants agree well with experimental data.

Pressure-dependent elastic constants are reported up to 150 kbar.

Abstract

We present a systematic ab initio study of the thermoelastic properties of hcp osmium as functions of temperature and pressure within the quasi-harmonic approximation (QHA). The precision of the Zero Static Internal Stress Approximation (ZSISA) and of the volume-constrained ZSISA (V-ZSISA) are rigorously assessed. For osmium, we find negligible deviations between ZSISA and a full free energy minimization (FFEM) approach. Also, the V-ZSISA approximation influences the results very little, as we found already in beryllium, despite the markedly different behavior of the c/a ratio with temperature in the two metals. Our QHA-derived ECs show excellent agreement with available experimental data in the temperature range of 5-301 K, outperforming the results obtained from the quasi-static approximation (QSA). Additionally, we report the pressure-dependent QHA ECs at 5 K, 301 K, and 1000 K, spanning pressures from 0 to 150 kbar.