Energy band structure and optical properties of $\mathrm{LiNaSO}_{4}$ crystals

The energy band structure of a $\mathrm{LiNaSO}_{4}$ has been calculated within the framework of density functional theory for space group $P31c$. It has been established that bandgap width $E_g$ in the GGA approximation is $5.49$ eV. The valence band top is generally formed of oxygen $p$-electrons, while the conduction band bottom is composed of lithium and sodium $s$-states. The effect of the cationic substitution $\mathrm{Na}\to\mathrm{K}\to\mathrm{Rb}\to\mathrm{NH}_{4}$ on the electron structure of $\mathrm{LiNaSO}_{4}$ group crystals is considered. Based on the calculated dielectric functions, the spectral dependences of the refractive indices and extinction coefficient of a crystal were calculated and compared with experimental data.