Theoretical surface morphology of {0 1 1¯ 2} acute rhombohedron of calcite: A comparison with experiments and {1 0 1¯ 4} cleavage rhombohedron

Theoretical surface profiles of the {011¯2} form of calcite crystal are drawn by applying the Hartman-Perdok method that allows to build non-polar outermost crystal layers without imposing arbitrary surface reconstructions. Profiles consistent with the bulk crystal symmetry are showed to correspond to minima of the surface energy for both the Ca2+ and CO32− terminated profiles. To take into account the interface vibration entropy and the energy of water adsorption is crucial to evaluate the relative variations of the surface free energy of {0 1 1¯ 2} and {1 0 1¯ 4} rhombohedra with temperature and to explain why both forms can make the equilibrium shape of the crystal.Furthermore, the calculation of the edge energies allows to account for the surface patterns observed on both rhombohedra.