The calculated phonon spectra of the three GeSe phases (Figure ) show similar features, with the notable exception that the PDoS of Pnma and R3m GeSe shows contributions from both atoms across the full range of phonon frequencies. Similarly, while there is some "splitting" in the PDoS of rocksalt GeSe, it is less prominent than in GeS. The extent of the splitting can be attributed to both the mass differences between Ge and S/Se, and to the nature of the bonding in the different structure types. Comparison of the spectra of GeS and GeSe also shows that the latter span a narrower range of frequencies, which is primarily due to the inverse relationship between frequency and atomic mass.