Theoretical structure and surface energy of the reconstructed {01.2} form of calcite (CaCO3) crystal

The surfaces energies (γ) at 0 K, for relaxed and unrelaxed (01.2)R1Ca, (01.2)R1CO3, (01.2)R2Ca and (01.2)R2CO3 faces, were determined either at DFT level or by using empirical potentials. Independently of the method of calculation employed, the stability order of the relaxed faces is (01.2)R1CO3 < (01.2)R2Ca < (01.2)R2CO3 < (01.2)R1Ca. Concerning the unrelaxed faces, whose energies were evaluated by using empirical potentials only, the stability order is instead (01.2)R1Ca < (01.2)R2Ca < (01.2)R1CO3 < (01.2)R2CO3; such different ordering shows the importance of geometry relaxation in the calculation of the surface energy. The values of the relaxed surface energies are γ(01.2)R1CO3≈750, γ(01.2)R2Ca≈950, γ(01.2)R2CO3≈980 and γ(01.2)R1Ca≈1050 erg/cm2.