Jorge O. Sofo, Department of Physics Department of Materials Science and Engineering and Materials Research Institute The Pennsylvania State University

Abstract: Transport Coecients Beyond the Relaxation Time Approximation with a Memory Function Approach.

For the calculation of transport coecients, the Kubo formula is exact to linear order in the excitation as long as we have the exact Hamiltonian. As we do not have it, the goal is to and approximations that capture physical phenomena of interest such as quantum coherence and localization and, at the same time can be incorporated into our ground-state, successful, and omnipresent DFT codes. We present an ab-initio method for the evaluation of transport coecients from electronic structure calculations that goes beyond the relaxation time approximation. The method evaluates the Kubo linear-response formula treating the scattering mechanisms to innite order using a memory function approach. It can be incorporated into any code that calculates the non-interacting space and time dependent charge-charge correlation function. We have done the implementation in the Exciting code. As a proof of principle, we calculate the conductivity of sodium limited by static disorder. This self-consistent approach describes the localization of the carriers in this simple metal for strong disorder. In comparison with the relaxation time approximation, our method describes the Anderson localization of the system and corrects the overestimation of the conductivity in the metallic phase.