# Splitting up entropy into vibrational and configurational contributions in bulk metallic glasses: A thermodynamic approach

## TL;DR

This paper introduces a versatile thermodynamic methodology using molecular dynamics to separate vibrational and configurational entropies in bulk metallic glasses without requiring a crystalline phase, applicable to various materials.

## Contribution

The authors develop a novel, crystalline-phase-independent approach to decompose entropies in metallic glasses, validated on Cu-Zr alloys and applicable to any material.

## Key findings

- The method accurately estimates vibrational and configurational entropies in metallic glasses.
- Configurational entropy is significantly higher in Al-containing glass, correlating with glass-forming ability.
- Results align with experimental data, validating the methodology.

## Abstract

We applied an efficient methodology to separate vibrational and configurational entropies in bulk metallic glasses by means of molecular dynamics simulation based on a combination of non-equilibrium adiabatic switching and reversible scaling methods. This approach involves calculating the vibrational free energy using the Einstein crystal as a reference for the solid phase and the recently proposed Uhlenbeck-Ford model for the fluid phase. This methodology has the advantage that it does not require a crystalline solid phase for separating the entropies. Therefore, in principle, it is applicable to any material, regardless of whether or not it has a crystalline phase. Using this methodology, we separate the vibrational and configurational entropies of two metallic glasses with different fragilities at zero external pressure, namely, Cu$_{50}$Zr$_{50}$ and Cu$_{46}$Zr$_{46}$Al$_{8}$. We find that the results for the former alloy are in quite reasonable agreement with recent experimental work by Smith \textit{et al.}[H. L. Smith \textit{et al.}, Nat. Phys. \textbf{13}, 900 (2017)]. We also find the configurational entropy of the glass containing Al to be 70\% larger than that of the other glass. Our results suggest that, although other factors may be at play, the configurational entropy can be used to investigate the effect of the addition of a minor-alloying element on the glass-forming ability of bulk metallic glasses.