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A classical interatomic force field for hydroxyapatite has been parameterized from periodic ab initio calculations carried out on the hexagonal structure (space group P63). The GULP program has been used for fitting geometry and phonon frequencies computed with the CRYSTAL06 program using the B3LYP hybrid functional and Gaussian-type basis set of polarized double zeta quality. Polarization effects and covalent bonding have been included through the shell-ion model potential. Excellent agreement has been found in reproducing structural features, lattice dynamics, the OH stretching vibrations and relative phase stabilities between the monoclinic structure (space group P21/b) and the hexagonal one. Transferability from hydroxyapatite to other calcium phosphates has also been demonstrated. [ABSTRACT FROM AUTHOR]

Both glycine and water exhibit a high affinity towards the hydroxyapatite HA surfaces. What happens when they are co-adsorbed at the HA (001) surface? B3LYP periodic calculations reveal that glycine displaces the pre-adsorbed water interacting directly with the HA surface. [ABSTRACT FROM AUTHOR]