Electronic and energy structure of valence electrons of arsenate apatites of calcium and cadmium

Electronic structure of arsenate compounds is studied using the full potential APW + lo method. The degrees of distortions of AsO4 tetrahedra for these compounds with respect to the Td point group are analyzed by means of relaxations of atomic positions. The behavior of the electronic density in space coordinates is investigated using Bader's analysis of atoms in molecules. Apatites in the form of Ca10(AsO4)6X2, where X = F, Cl, OH, are established to decrease band gap widths by 1.5 - 2.0 eV, when calcium is substituted for cadmium. Apatites in the form of Ca10(AsO4)6X2, where X = F, Cl, OH, are established to decrease the bond strength of As-O bond under the substitution of calcium for cadmium due to both a decrease of degrees of the overlap of partial densities of states of oxygen and arsenic atoms and a decrease of the electronic charge flow from arsenic to oxygen.