  The structural, electronic, and optical properties of a recently synthesized
thorium compound Rb2Th7Se15 have been calculated in the density functional
theory framework for the first time. The calculated direct band gap was 1.471
eV (generalized gradient approximation) and 1.171 eV (local density
approximation), with both results being close to the experimental result of
1.83 eV. High covalency/iconicity of the Th-Se/Rb-Se bonds was demonstrated by
calculating effective Mulliken charges of all ions. The polarized calculations
of the complex dielectric function are presented; dependence of the calculated
index of refraction was fitted to the Sellmeyer equation in the wavelength
range from 500 to 2500 nm.
