Ab initio high pressure and temperature phase diagram of Au

High pressure behaviour of gold is of fundamental interest since it is used as a calibration standard in experiments. However, recent ab initio [1-2] and experimental studies [3-5] show diverging solid phase stability domains. To simulate materials under extreme conditions that experiments cannot reach and that the existing numerical potentials fail to reproduce, Ab Initio Molecular Dynamics (AIMD) is the most appropriate method. Unfortunately, it is highly time consuming and therefore too prohibitive to build a complete phase diagram. Alternative methods exist, as the quasi-harmonic approximation[1] but its validity at high temperature is difficult to assess. Here to clarify conflicting results between experiments and simulations we use the Machine Learning Assisted Canonical Sampling (MLACS) [6], which accelerates AIMD by two orders of magnitude while maintaining an ab initio accuracy. We used MLACS and thermodynamic integration to extract Gibbs free energies of fcc, bcc and hcp phases, and built the phase diagram of Au between 0 and 1 TPa and from 0 K to 10 000 K. Our phase diagram is in agreement with the most recent experiments[4].



References:

[1] N. Smirnov, J. Phys. Condens. Matter 29, 105402 (2017)

[2] T. Ishikawa et al, Phys. Rev. B 88, 214110 (2013)

[3] L. Dubrovinsky et al. Phys. Rev. Lett. 98, 045503 (2007)

[4] A. Dewaele et al. Nature Communications 9, 2913 (2018)

[5] Briggs et al. PRL, 123, 045701 (2019)

[6] A, Castellano et al. Phys. Rev. B 106, L161110 (2022)