6. Ab Initio Modelling of the Structure and Properties of Crystalline Calcium Carbonate

Many biominerals occur as crystalline materials, and their formation often involves steps where metastable crystalline phases appear. The latter can correspond either to intermediate species that then transform into more stable phases or to the final mineral crystal. Because of their instability and rare occurrence, the structure and properties of such intermediate metastable phases may not always be fully understood from experiment alone. Vaterite (CaCO₃) is one such phase, and recent advances in understanding its complex structure were achieved through ab initio modelling techniques. This chapter will highlight the importance of achieving a comprehensive understanding of the atomic details of the crystalline phases involved in biomineralisation. Examples will be focused on calcium carbonate, and especially on vaterite, and ab initio methods based on density functional theory (DFT) will be proposed as the main tool to undertake this kind of investigation, together with more traditional techniques such as spectroscopic methods, microscopies and X-ray and neutron diffraction.