Ab Initio study of the electronic and optical properties of hexagonal and cubic Ge2Sb2Te5

Abstract

The electronic and optical properties of hexagonal and cubic Ge 2 Sb 2 Te 5 have been calculated using the QUANTUM ESPRESSO and Yambo codes. The study has considered the variation of electronic band gaps with lattice constants using the LDA with non-linear correction, where it was established that both phases are apparently metallic at equilibrium. Upon increasing a, it was found that the hexagonal phase had a maximum gap of 0.22 eV at a c/a value of 3.49 whereas the cubic phase had a maximum gap of 0.23 eV at a much higher c/a value of 10.62. Findings of the optical absorption spectra of both hexagonal and cubic Ge 2 Sb 2 Te 5 obtained using time dependent density functional theory (TDDFT) and the partially self-consistent GW (GW 0 ) are also reported. The absorption edge has been observed at 0.48 eV using TDDFT and at 0.21 eV using GW 0 for the hexagonal phase.