ELECTRONIC STRUCTURE AND OPTICAL SPECTRA OF AG3SBS3 CRYSTAL IN THE MONOCLINIC PHASE
DOI:
https://doi.org/10.32782/pet-2024-1-5Keywords:
semiconductor, pyrargyrite, density functional theory, band structure, dielectric functionAbstract
The work is devoted to the theoretical study of the features of the structure, electronic states, and optical properties of the ternary chalcogenide semiconductor Ag3SbS3, which has a crystal structure with a space group of symmetry P21/с. The study was conducted using the methodology from first principles. Calculations were carried out within the framework of the density functional theory (DFT) and the Kohn-Sham formalism using the local density approximation and the generalized gradient approximation to describe the exchange-correlation interaction between electrons. In order to find the equilibrium parameters of the lattice and the atomic coordinates, before calculating the properties of the crystal, a geometric optimization of the crystal structure was carried out using the Broyden-Fletcher-Goldfarb-Schenno algorithm. The theoretically obtained structural parameters of the crystal are in good agreement with the experimental data. For the first time, the band-energy structure of the Ag3SbS3 crystal in the monoclinic phase was studied. It was found that the E(k) band structure is characterized by a relatively weak dispersion of the conduction band and valence band levels. The top of the valence band is formed by a wide band from 0 to –5 eV. The band gap is of an indirect type. The calculated values of the band gap Eg are 1.1 eV for LDA and 1.4 eV for GGA functionals. The structure of the electronic levels of the investigated compound was analyzed from the calculations of the full and partial density of states of the crystal. It was found that the top of the valence band is formed by p-states of sulfur and antimony atoms. The bottom of the conduction band is formed by equal s-states of silver and p-states of Sb. A significant similarity between the electronic structure of the crystal in the monoclinic phase and the tetragonal phase is shown. Milliken charges and bond occupancy were calculated, which confirmed their ionic-covalent nature. The optical spectra of the Ag3SbS3 crystal in the monoclinic phase were calculated and analyzed.
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