Surface reconstructions and relaxation effects in a centre-symmetrical crystal: the {00.1} form of calcite (CaCO3)

Reconstructing polar surfaces of crystals represents the pathway needed to obtain both surface stability and minimum of surface free energy. Knowing these equilibrium conditions is, in turn, necessary to interpret surface kinetics, especially when foreign adsorption or epitaxial phenomena are involved. Here we reconstructed the {00.1} dipolar surfaces of a centre-symmetrical crystal, calcite (CaCO3), either by removing one half of the ions in the outermost layer of the face, or by applying calcite to the octopolar Lacmann's model, already proposed for NaCl-like lattices. This second way respects the bulk symmetry of the crystal and was carried out by removing 3/4 of the ions in the outermost layer and 1/4 in the second to last one, respectively. Relaxed and athermal surface energies were determined at the empirical level and the octopolar CO3 terminated {00.1} form was the most stable. Moreover, calculation shows that the {00.1} form, along with the {10.4} and {01.2} rhombohedra, can enter the athermal equilibrium morphology of the calcite crystal. Finally, when recollecting our results on the reconstructed {01.2} form of calcite and {111} NaCl octahedron, it can be stressed that the bulk crystal symmetry has to be considered if one aims to achieve the self consistency of the surface reconstruction (Curie's principle).