Molecular dynamics simulations of phosphate-based glasses P2O5-CaO-Na2O have been carried out, using an interatomic force field that has been parameterized to reproduce the structural and mechanical properties of crystalline phosphorus pentoxide,

$\emph {o}^{\prime }$
o(P2O5) 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
${\rm DL}{\_}{\rm POLY}$
DL _ POLY
code (version 2.20) was used to model the high temperature shell dynamics. Structural characterizations of three biomedically applicative molar compositions, (P2O5)0.45(CaO)x(Na2O)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 Ca2+ 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.

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See supplementary material at http://dx.doi.org/10.1063/1.4770295 for the GULP input file for the static optimization of NaCaPO4 and the
${\rm DL}{\_}{\rm POLY}$
DL _ POLY
files: CONTROL, FIELD, and TABLE (ammended Os-Os Buckingham30 potential) for molecular dynamics simulations of the P45C30N25 PBG composition. Core-shell frictional damping was set at c2 = 20 for all temperatures of each glass quench, other than those run at 2500 K, which were parameterized at 20 ⩽ c2 ⩽ 23.

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