Crystalline ${\mathrm{As}}_2$${\mathrm{Se}}_3$: Electronic and geometric structure

Realistic ab initio total-energy calculations are performed to investigate the electronic and geometric structure of crystalline ${\mathrm{As}}_2$${\mathrm{Se}}_3$. Results include the following: total energies for various distortions, the equilibrium geometric structure, intralayer and interlayer cohesive energies, charge densities, the density of states, the band structure, rigid-layer phonon frequencies, and effective masses. Specific attention is focused on studying the nature of bonding within and between layers, as well as elucidating the nature of the electron and hole wave functions in the vicinity of the fundamental gap. In particular it is found that the interactions between the layers are crucial in determining the properties of the wave functions at the band edges. Moreover, the electron and hole masses are predicted to exhibit a large and unusual anisotropy.