Lattice Dynamics and Thermal Equation of State of Platinum

TL;DR

This study uses density functional theory to accurately calculate the thermal equation of state of platinum up to 550 GPa and 5000 K, improving pressure calibration standards.

Contribution

It provides a comprehensive DFT-based thermal EOS for platinum, incorporating various functionals and electronic temperature effects, enhancing calibration accuracy.

Findings

LDA results align best with experimental data.

Developed a consistent thermal EOS for platinum.

Extended EOS data up to 550 GPa and 5000 K.

Abstract

Platinum is widely used as a pressure calibration standard. However, the established thermal EOS has uncertainties, especially in the high $P$-$T$ range. We use density functional theory to calculate the thermal equation of state of platinum, up to 550 GPa and 5000 K. The static lattice energy is computed by using the LAPW method, with LDA, PBE, and the recently proposed WC functional. The electronic thermal free energy is evaluated using the Mermin functional. The vibrational part is computed within the quasi-harmonic approximation using density functional perturbation theory and pseudopotentials. Special attention is paid to the influence of the electronic temperature to the phonon frequencies. We find that in overall LDA results agree best with the experiments. Based on the DFT calculations and the established experimental data, we develop a consistent thermal EOS of platinum as a reference for pressure calibration.