Electronic band structure, charge density distribution and chemical bonding in molecular crystals of chalcogens

The electronic band structure and the charge density distribution are theoretically studied in rhombohedral and monoclinic selenium, rhombohedral and orthorhombic sulphur with the aim to classify types of chemical bonding in molecular crystals of chalcogens. It is found that valence s- and lower in energy p-electrons contribute mainly in covalent bonds between nearest neighboring atoms in ring-shaped molecules, while all types of valence p-electrons provide bonding between rings of atoms in crystals. Parameters of critical points and the character of the charge density distribution in their vicinity point to coexistence of a number of types of chemical bonding in molecular crystals of Se and S: covalent, semimetallic and one more type, characterizing by the charge density fluctuations. Van der Waals forces, being important for finding equilibrium lattice parameters, have little impact on the charge density distribution and on the chemical bonding in crystals of chalcogens. Keywords: chalcogens, molecular crystals, electronic band structure, types of chemical bonding.