Ab initio calculations of thermal conductivities in crystals

The calculations of thermal conductivity requires to know anharmonic properties of the crystal. For this purpose a non-perturbative anharmonic theory is applied, which do not make use of the potential energy expansion over atomic displacements, but instead, runs ab initio calculations of Hellmann-Feynman forces for atomic patterns of atoms with specific displacements to rebuild the anharmonic phonon frequencies, and group velocities. see [K.Parlinski, Phys.Rev. B 98, 054305 (2018),] The Green-Kubo equation for the thermal conductivity needs to know the above quantities and the phonon relaxation times, which are related to the 4th-order phonon correlation function expressed in terms of phonon anihilation and creation Bose operators. In currect formulation of anharmonic theory the relaxation times can be derived as analitical expression. The Green-Kubo formulae was succesfully applied to find thermal conductivity of Si and conductivities, related to the phonon and elastic waves, respectivily, were computed.

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