Electronic structure, chemical bonding features, and electron charge density of the double-cubane single crystal [Sb7S8Br2](AlCl4)3

The present calculations were performed using all-electron full potential linearized augmented plane wave method based on the density functional theory. We have optimized the structure of the double-cubane single crystal [Sb7S8Br2](AlCl4)3, starting with the x-ray diffraction data Zhang et al., [J. Am. Chem. Soc. 131, 9896 (2009)] , by minimization of the forces (1 mRy/au) acting on the atoms, keeping the lattice parameters fixed at the experimental values. Our calculations show that [Sb7S8Br2](AlCl4)3 possesses a wide indirect energy band gap of about 1.6 eV (2.03 eV) using local density approximation (Engel–Vosko generalized gradient approximation) exchange correlation potentials. To describe the bonding properties we have evaluated the electronic charge space density contour in four planes-namely (001), (110), (100), and (010) which show that this compound possesses a considerable anisotropy. The contour plot shows partial ionic and strong covalent bonding between S–Sb, Al–Cl, S–Br, S–S, Cl–Cl, and Sb–Br atoms