A computer modelling study of the uptake and segregation of fluoride ions at the hydrated hydroxyapatite (0001) surface: introducing a Ca10(PO4)6(OH)2 potential model†
Abstract
A combination of electronic structure calculations and interatomic potential-based methods are employed to study the uptake and segregation of fluoride ions from solution into the hydroxyapatite lattice. The hydroxyapatite potential model derived for this work accurately reproduces experimental properties and relative enthalpies of formation and is further validated by Density Functiontional Theory calculations of fluoride defects in bulk hydroxyapatite. Calculations of solid solutions of fluor- and hydroxy-apatite show that hydroxy groups are easily replaced by fluoride ions on thermodynamic grounds (ΔEx = −0.4 to −6.4 kJ mol−1), forming sheets of fluoride in the a/b plane. Molecular Dynamics simulations of the incorporation of fluoride into hydroxyapatite show that fluoride ions are also easily incorporated from solution into the surface of hydroxyapatite (ΔE = −193 kJ mol−1), but they do not segregate into the bulk crystal beyond approximately 10 Å. The