Electronic structure of crystalline phosphorus pentoxide and the effect ofan Ag impurity

The phosphorus pentoxide crystal with Pnam symmetry containing four P2O5 mo lecules in the unit cell was calculated by ab initio density-functional the ory in the local-density approximation with a plane-wave basis set using th e CASTEP code. The calculated optimized geometry is in good agreement with experiment. The population analysis made in terms of Lowdin and Mulliken ch arges and Wiberg indexes showed that this crystal has a mixed chemical bond ing, partly ionic, partly covalent. An Ag atom impurity in the phosphorus p entoxide crystal was investigated within the periodic model. The distortion of the lattice around the impurity was analyzed in terms of PO4 tetrahedra . The calculations showed that in spite of considerable deformation of the lattice, the Ag impurity does not break the P-O bonding network and changes the P-O bond order only a little. The Ag impurity atom is bound to the cry stal with an almost pure ionic bond, the Ag atomic charge being 0.6 (Lowdin charge).