Electronic and structural properties of superionic Cu$_{2}$Se from density functional theory

The superionic high temperature phase of Cu$_{2}$Se has been found to yield high thermoelectric efficiency due to an interesting combination of low thermal conductivity and a rather high power factor. The low thermal conductivity has been found to be due to the quasi-liquid behaviour of the superionic Cu atoms (Liu et al., Nature Materials, {\bf11}, 422-425 (2012)). Here we will present results obtained using density functional theory calculations of the electronic and structural properties of the superionic Cu$_{2}$Se phase. We will especially address how the inclusion of non-local exchange by the use of hybrid density functionals as well as how localization of the Cu 3d-states affect the electronic structure of Cu$_{2}$Se.