J Phys Condens Matter. 2016 Apr 13;28(14):145401. doi: 10.1088/0953-8984/28/14/145401. Epub 2016 Mar 14.

Free energy model for solid high-pressure phases of carbon.

Journal of physics. Condensed matter : an Institute of Physics journal

Manuel Schöttler, Martin French, Daniel Cebulla, Ronald Redmer

PMID: 26974530 DOI: 10.1088/0953-8984/28/14/145401

Abstract

Analytic free energy models for three solid high-pressure phases--diamond, body centered cubic phase with eight atoms in the unit cell (BC8), and simple cubic (SC)--are developed using density functional theory. We explicitly include anharmonic effects by performing molecular dynamics simulations and investigate their density and temperature dependence in detail. Anharmonicity in the nuclear motion shifts the phase transitions significantly compared to the harmonic approximation. Furthermore, we apply a thermodynamically constrained correction that brings the equation of state in accordance with diamond anvil cell experiments. The performance of our thermodynamic functions is validated against Hugoniot experiments.

Publication Types

• Journal Article
• Research Support, Non-U.S. Gov't