First-Principles Thermodynamics of Al$_{10}$V: An Analytical Treatment of Localized Anharmonic Modes

TL;DR

This paper introduces a first-principles framework to accurately model localized anharmonic vibrations in Al$_{10}$V, improving thermodynamic predictions and explaining experimental anomalies related to phase stability and thermal properties.

Contribution

It develops a novel numerical approach to incorporate strongly anharmonic modes into thermodynamic calculations, surpassing the harmonic approximation for complex intermetallics.

Findings

Reproduces experimental anomalies in thermal expansion and specific heat.

Shows guest atoms are crucial for phase stabilization at high temperatures.

Demonstrates the importance of anharmonic effects in thermodynamic modeling.

Abstract

Many complex intermetallic structures possess cage-like environments that can host additional guest atoms. In Al$_{10}$V, these atoms give rise to low-frequency, localized vibrations (Einstein modes) that dominate the thermodynamic response at low temperature. They become imaginary under volume expansion as temperature rises, invalidating the harmonic approximation. We develop a framework to incorporate these strongly anharmonic vibrational modes into first-principles thermodynamic calculations. By explicitly modeling the cage potential and solving the associated Schr\"odinger equation numerically, we compute the full anharmonic free energy contribution and demonstrate its impact on thermodynamic phase stability. Our results reproduce key experimental signatures, including the anomalous rise in the thermal expansion coefficient and specific heat at low temperatures, and reveal that the presence of guest atoms is essential to stabilizing the Al$_{10}$V phase at elevated temperatures.