Polarizable force field development and molecular dynamics study of phosphate-based glasses

Abstract

Molecular dynamics simulations of phosphate-based glasses P(2)O(5)-CaO-Na(2)O have been carried out, using an interatomic force field that has been parameterized to reproduce the structural and mechanical properties of crystalline phosphorus pentoxide, o(')(P(2)O(5))(∞) orthorhombic phase. Polarization effects have been included through the shell-model potential and formal charges have been used to aid transferability. A modification to the DL_POLY code (version 2.20) was used to model the high temperature shell dynamics. Structural characterizations of three biomedically applicative molar compositions, (P(2)O(5))(0.45)(CaO)(x)(Na(2)O)(0.55-x) (x = 0.30, 0.35, and 0.40), have been undertaken. Good agreement with available experimental and ab initio data is obtained. The simulations show that, dependent on composition, the phosphorus atoms are primarily bonded to two or three oxygens that in turn bridge to neighbouring phosphorus atoms. Na(+) and Ca(2+) modifiers are found to occupy a pseudo-octahedral bonding environment with mean oxygen coordination numbers of 6.55 and 6.85, respectively, across all compositions studied.