Phonon interactions in rock salt and fluorite structures

Space group irreducible derivatives of the Born Oppenheimer potential are computed from density functional theory for materials with the rock salt and fluorite structures, including PbTe and ThO2. We utilize our recently developed group theoretical approach which allows the extraction of the irreducible derivatives from finite displacement calculations on the smallest possible supercells using the smallest possible number of calculations. Quadratic (i.e. phonons), cubic, and quartic irreducible derivatives have been computed. The fidelity of the irreducible derivatives is tested via comparison to strain derivatives of the phonons. Both dynamics and thermodynamics are evaluated using our irreducible Taylor series, yielding observables such as phonon linewidths, thermal conductivity, thermal expansion, mean square displacements, etc. Results on PbTe and ThO2 are compared to experiment.