Quasiharmonic approximation via irreducible derivatives: low symmetry crystals
ORAL
Abstract
The quasiharmonic approximation is a standard approach to include anharmonicity when evaluating temperature-dependent vibrational observables, yet computing arbitrary observables is nontrivial. Here we execute the irreducible derivative approach to the quasiharmonic approximation, greatly reducing the computational cost and facilitating the study of lower symmetry crystals. Specifically, we study PbTiO$_3$ using density functional theory within various exchange-correlation functionals, computing the thermal expansion and the full elastic constant tensor as a function of temperature. The Born-Oppenheimer potential and the irreducible components of the dynamical matrix are parametrized by a Taylor series expansion in symmetrized strain, allowing for the systematic study of successively higher order truncations of the quasiharmonic potential. Additionally, we explore the validity of the quasiharmonic approximation in metals, including ZrN. Results are compared to existing experimental measurements.
*This research was supported by the Center for Thermal Energy Transport Under Irradiation (TETI), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. This work was supported by the grant DE-SC0016507 funded by the U.S. Department of Energy, Office of Science. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
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Presenters
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Mark Mathis
- Columbia University