Local ordering of hydroxy groups in hydroxyapatite

Density functional theory calculations of hydroxyapatite identified the oxy gen and hydrogen positions of the hydroxy groups in the crystal structure t o be well defined, alternating in a column in the c-direction, and we predi ct that the experimentally found oxygen and hydrogen disorder is due to the presence in the crystal of differently oriented locally ordered domains, a finding which is important for studies of crystal growth and surface react ivity.