Ab initio calculations of band structure and thermophysical properties for SnS2 and SnSe2

The electronic band structure and elastic constants of SnS2 and SnSe2 have been calculated by using density-functional theory (DFT). The calculated band structures show that SnS2 and SnSe2 are both indirect band gap semiconductors. The upper valence bands originate mainly from Sp and Snd electrons, while the lowest conduction bands are mainly from (S, Se) p and Sns states. The calculated elastic constants indicate that the bonding strength along the [100] and [010] direction is stronger than that along the [001] direction and the shear elastic properties of the (010) plane are anisotropic for SnS2 and SnSe2. Both compounds exhibit brittle behavior due to their low B/G ratio. Relationships among volumes, the heat capacity, thermal expansion coefficients, entropy, vibrational energy, internal energy, Gibbs energy and temperature at various pressures are also calculated by using the Debye mode in this work.