Ab initio calculations of the band structure and optical properties of Ag7SiS5I

In this paper the method of the density functional theory in the local electron density approximation with allowance for strong correlations in the d-shell of the noble metal ion (LDA+U method) calculations are performed of the band structure, the partial densities of electronic state and optical functions: dielectric permeability, refractive index, reflection and absorption coefficients of Ag7SiS5I crystal. According to the calculation results Ag7SiS5I is a indirect-gap semiconductor with the calculated energy of the band gap Egicalc=1.73eV. The analysis of partial contributions into the density of electronic states allowed to identify the genetic origin of different subbands of the valence band, and also to obtain the formation of a chemical bond in the crystal under study. The most important feature of the electronic spectrum of the Ag7SiS5I crystal is the presence of an intense peak in the density of states N(E) formed by Ag4d-like zone. The calculated spectral dependences of the absorption and reflection coefficients show the main features of the e2(ω) dependence, and the maxima of the energy distribution of the refractive index practically coincide in position with the centers of gravity of the bands of the real part of the complex permittivity.