Theoretical insights into the chemical bonding, electronic structure, and spectroscopic properties of the lanarkite Pb$_2$SO$_5$ structure

This article provides a comprehensive investigation on the chemical bonding, electronic structure, and spectroscopic properties of the lanarkite-type PSO structure from a computational perspective. Thus, different functionals in the field of DFT (e.g., PBE, PBE0, PBESOL, PBESOL0, BLYP, WC1LYP and B3LYP) using a triple-zeta valence plus polarization basis set were assessed to accurate prediction their fundamental properties. Among all DFT functionals tested in this study, in particular, the PBE was the one that showed the best agreement with the experimental data available in the literature. Our results also reveal that the [PbO$_5$] clusters are formed with three different Pb--O bond lengths, with values of about 2.32, 2.59 and 2.84\AA, respectively, and the [SO$_4$] clusters have the same S--O bond length of 1.57\AA. We then performed a complete topological analysis of this system to better understand these structural differences. Additionally, the PSO structure has an indirect band gap energy of 2.9 eV and an effective mass ratio of about 0.415 (using PBE calculations) which may, in principle, indicate a low recombination of electro-hole pairs in the lanarkite structure. Therefore, we believe that a detailed understanding of their electronic structure and spectroscopic properties as well as their chemical bonding is critically important for developing new technologies based on PSO.