We present a comprehensive computational study on the properties of facecentered cubic and hexagonal chalcogenide Ge 2 Sb 2 Te 5 . We calculate the electronic structure using density functional theory (DFT); the obtained density of states (DOS) compares favorably with experiments, also looking suitable for transport analysis. Optical constants including refraction index and absorption coefficient capture major experimental features, aside from an energy shift owed to an underestimate of the band gap 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 ∼ 1.4 × 10 6 J/(m 3 K) at high temperature, in agreement with experimental data, and provides insight into the low-temperature range (< 150 K), where data are unavailable.

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