Thermodynamics and Thermal Conduction at Extreme Conditions Based on Phonon Quasiparticles*

Predictions of materials properties at extreme conditions of pressures and temperatures are exceedingly important because it is challenging to obtain them experimentally. At the atomistic level, the accuracy of these predictions relies essentially on a satisfactory characterization of lattice anharmonicity which is generally pronounced at high temperatures. This has stimulated the development of several ab initio approaches to address anharmonic effects on lattice vibrations.

In this talk we present an overview of an ab initio method to address lattice anharmonicity based on the concept of phonon quasiparticles and illustrate its applications to some complex systems, e.g., (i) the vibrational and thermodynamic stabilization of cubic CaSiO3-pv at high temperatures, (iii) the hcp-bcc pre-melting transition in beryllium, and (iii) the irregular thermal shifts of IR frequencies and the breakdown of the well-known minimal phonon mean free path theory in MgSiO₃-perovskite. We also introduce a computational package for high pressure and high temperature computational studies that interfaces with popular ab initio packages.

References:
Z. Zhang, D.-B. Zhang, T. Sun, and R. M. Wentzcovitch, Computer Physics Communications (2018, under review)
D.-B. Zhang, P. B. Allen, T. Sun and R. M. Wentzcovitch, Physical Review B RC, 96, 100302 (2017).
Y. Lu, T. Sun, Ping Zhang, P. Zhang, D.-B. Zhang, and R. M. Wentzcovitch, Physical Review Letters 118, 145702 (2017).
D.-B. Zhang, T. Sun and R.M. Wentzcovitch, Physical Review Letters 112, 058501 (2014).
T. Sun, D.-B. Zhang, and Renata M. Wentzcovitch, Physical Review B 89, 094109 (2014).