CO32– Mobility in Carbonate Apatite As Revealed by Density Functional Modeling

Carbonate apatite is a material of the utmost importance as it represents the inorganic fraction of biological hard tissues in bones and teeth. Here we study the static and dynamic features of CO32– ion in the apatitic channel of carbonate apatite (A-type substitution), by applying both static and dynamic quantum mechanical calculations based on density functional methods with B3LYP-D* and PBE functionals. The static calculations reveal a number of almost energetically equivalent carbonate configurations in the channel, leading to cell parameters compatible with the P3̅ space group assigned by the experimental X-ray structure determination. Ab initio isothermal–isobaric molecular dynamics simulations provide insights on the CO32– mobility, showing that at the temperature of the experimental structural determination the CO32– moiety undergoes a dynamic disorder, as the carbonate group is almost free to move within the apatitic channel enhancing its exchangeability with other anions.