Electronic, Optical and Thermal Properties of the Hexagonal and Rock Salt-Like Ge2Sb2Te5 Chalcogenide from First Principle Calculations

We present a comprehensive computational study on the properties of rock salt-like and hexagonal chalcogenide Ge2Sb2Te5 supported by experimental data. We calculate the electronic structure using density functional theory (DFT); the obtained density of states (DOS) compares favorably with experiments, and is suitable for transport analysis. Optical constants including refractive index and absorption coefficient capture major experimental features, aside from an energy shift owed to an underestimate of the bandgap that is typical of DFT calculations. We also compute the phonon DOS for the hexagonal phase, obtaining a speed of sound and thermal conductivity in good agreement with the experimental lattice contribution. The calculated heat capacity reaches approx. 1.4 x 10^6 J/(m^3 K) at high temperature, in agreement with experiments, and provides insight into the low-temperature range (<150 K), where data are unavailable.