Ab initio quantum-mechanical modeling of the (0 0 1), (1¯01) and (1 1 0) surfaces of zabuyelite (Li2CO3)

Bulk and (0 0 1), (1¯01) and (1 1 0) slab geometry optimizations of zabuyelite (Li2CO3) were performed at Hartree-Fock (HF) and DFT levels. The (0 0 1) and (1¯01) slabs showed an higher surface relaxation with respect to the (1 1 0) slab. The CO3 groups in the top surface layer of (0 0 1) and (1¯01) slabs are strongly tilted with respect to their position in the bulk, tending to arrange parallel to the respective faces. On the contrary, a modest surface relaxation was observed for the (1 1 0) slab.The surface energies (γ) for relaxed and unrelaxed (0 0 1), (1¯01) and (1 1 0) faces, were determined at the HF and DFT levels. The values of the surface energy for the relaxed faces are: γ(001) = 160(HF)-180(DFT), γ(1¯01)=260-280 and γ(110) = 570-590 erg/cm2. For the unrelaxed faces the values of the surface energy result to be higher: γ(001) = 248-255, γ(1¯01)=392-399, γ(110) = 674-697 erg/cm2. Therefore, the stability order of relaxed and unrelaxed surfaces reads: (001)<(1¯01)<(110), as results from both HF and DFT calculations.