A density functional theory study of structural, mechanical and electronic properties of crystalline phosphorus pentoxide

Quantum mechanical calculations of single crystal phosphorus pentoxide [12pt]{minimal}{document}(P₂O₅){document}(P2O5) have been conducted using the plane-wave ultrasoft pseudopotential technique based on the density functional theory (DFT), in the generalized gradient approximation, with dispersive correction (DFT-D). The implementation of the dispersive correction is shown to improve significantly the structural agreement with experiment, compared to standard plane-wave DFT. The second order elastic constants for the [12pt]{minimal}{document}o(P₂O₅)∞{document}o′(P2O5)∞ and [12pt]{minimal}{document}o(P₂O₅){document}o(P2O5) orthorhombic phases were obtained from a polynomial fit to the calculated energy-strain relation. Both phases are shown to be highly elastically anisotropic due to structural features. Polycrystalline aggregate properties have been evaluated to give complete mechanical descriptions. Further investigation of the electronic band structure and density of states has been completed. Analysis of the complex chemical bonding has been carried out using Löwdin atomic charge and valence charge density data showing mixed ionic and covalent character in both phases.