Thermodynamic study of reconstructed crystal surfaces.: The octopolar (111) face of LiF crystals

Dipolar crystal faces, although reconstructed, have a high surface energy and are forbidden in a Wulff plot at 0 K, in a vacuum. However, they do grow far from equilibrium and due to the relatively open surface structure, are eligible for adsorption, epitaxy and incorporation of foreign substances. In this paper, we study the surface structure of the (111) dipolar face of LiF and calculate the thermal contribution to the surface energy, in the harmonic limit at the Hartree–Fock level. The surface energy calculated at 0 K, of the Li and F terminated (111) faces are 0.767 and 0.698 J/m2, respectively. When the vibrational energy and entropy are considered the surface energies at 298.15 K decrease to 0.720 (Li terminated) and 0.670 (F terminated) J/m2. Finally, when the configurational entropy is also taken into account, the surface energies are 0.663 (Li terminated) and 0.612 (F terminated) J/m2.