MR016-0002
pgm: A Python package for free energy calculation

Wednesday, 16 December 2020
Poster
Jingyi Zhuang1, Hongjin Wang2, Qi Zhang3, Zhen Zhang3 and Renata Wentzcovitch3,4, (1)Lamont - Doherty Earth Observatory, Department of Earth and Environmental Sciences, Columbia University in the City of New York, Palisades, NY, United States, (2)Columbia University in the City of New York, Department of Computer Science, New York, NY, United States, (3)Columbia University in the City of New York, Department of Applied Physics and Applied Mathematics, New York, NY, United States, (4)Columbia University in the City of New York, Lamont-Doherty Earth Observatory, Earth and Environmental Sciences, Applied Physics and Applied Mathematics Department, Palisades, NY, United States
Abstract:
The quasi-harmonic approximation (QHA) is a powerful method for computing free energy and thermodynamic properties of materials at high pressures (P) and temperatures (T). However, anharmonicity, electronic excitations in metals, or both, introduce an intrinsic T-dependence on the phonon frequencies, which makes the QHA inadequate. Here we present a Python package, pgm, for free energy and thermodynamic property calculations. It is based on the concept of phonon quasiparticles and the phonon gas model (PGM). The free energy is obtained by integrating the entropy, which can be readily calculated for a system of phonon quasiparticles. This method is useful for obtaining free energy in anharmonic insulators and harmonic or anharmonic metals. Calculations of thermodynamic properties and equations of state are also implemented in the code. We demonstrate successful applications of pgm to hcp-iron (ε-Fe) at extreme conditions and cubic CaSiO3-perovskite, a strongly anharmonic system.

*This research was supported by the Department of Energy grant DESC0019759.