First-principles investigation of the lattice dynamics of ε-GaSe

We have calculated the bulk-phonon dispersion of the layered semiconductor epsilon-GaSe using ab initio methods. In contrast to previous model calculations, our results show good agreement both with the phonon frequencies from neutron-scattering experiments as well as with the phonon-dispersion curves of the GaSe(0001) surface measured with inelastic He-atom scattering. We have also performed the calculation of the elastic constants C-13 and C-33 and the linear combination C-11 + C-12, in good agreement with experimental values. Furthermore, we have evaluated the equilibrium structure and the surface phonon frequencies at the (K) over bar point of the GaSe(0001) surface. We observed no surface relaxations, and only small differences between bulk and surface frequencies, supporting the fact that only weak interactions exist between the layers. [S0163-1829(98)02107-9].