Electronic, bonding, linear and non-linear optical properties of novel Li2Ga2GeS6 compound

• Li2Ga2GeS6 studied for the first time using first principles calculations.
• Different exchange correlation potentials have been adopted for the calculations.
• Bandgap of the compound is pseudo direct.
• Optical structures are prominent in the low frequency ultraviolet region.
• The lone pair basins seem to have a non-negligible role in the optical properties.

Recently a new sulphide compound Li2Ga2GeS6 was synthesized. It has attracted great attention due to its nonlinear optical properties. Quite surprisingly no theoretical study yet been reported on the physical properties of this important material. We have paid attention to study the electronic and optical properties of Li2Ga2GeS6 using first principles techniques of density functional theory. Different exchange-correlation techniques have been applied to study these properties. From local density and generalized gradient approximations the compound is predicted to be direct bandgap. However the band gap is indirect when calculated through the Engle–Vosko and modified Becke–Johnson potentials. Therefore the bandgap of the compound is pseudo direct (direct and indirect band gaps are very close). In optical properties dielectric function, refractive index, reflectivity and absorption coefficient were studied. Furthermore, the second harmonic generation properties of the compound are predicted.