Anharmonic Thermodynamics of Vacancies Using a Neural Network Potential

TL;DR

This paper develops a neural network potential for aluminum to accurately study anharmonic effects on vacancy formation free energies at high temperatures, revealing nonlinear entropy behavior and deviations from Arrhenius law above 600 K.

Contribution

It introduces a neural network potential that overcomes DFT limitations, enabling precise anharmonic thermodynamics calculations for vacancies in metals.

Findings

Anharmonicity significantly influences vacancy concentrations at high temperatures.

Vacancy formation free energy deviates from Arrhenius law above 600 K.

Vacancy formation entropy exhibits nonlinear temperature dependence.

Abstract

Lattice anharmonicity is thought to strongly affect vacancy concentrations in metals at high temperatures. It is however non-trivial to account for this effect directly using density functional theory (DFT). Here we develop a deep neural network potential for aluminum that overcomes the limitations inherent to DFT, and we use it to obtain accurate anharmonic vacancy formation free energies as a function of temperature. While confirming the important role of anharmonicity at high temperatures, the calculation unveils a markedly nonlinear behavior of the vacancy formation entropy and shows that the vacancy formation free energy only violates Arrhenius law at temperatures above 600 K, in contrast with previous DFT calculations.