Quantum-Mechanical and Thermodynamical Study on the (100) Face of LiF Crystals

In this work we determine the Helmholtz free energy ( F ) of the (100) face of LiF. It accounts for the athermal work of separation at 0 K, the vibrational and zero point surface energy, and the surface entropy. The thermal contributions to F are calculated via the vibrational partition functions obtained from the frequency spectrum of the infinite crystal and of slabs limited by (100) faces. The vibrational frequencies and modes are calculated using the CRYSTAL06 software for quantum-mechanical ab initio calculations. The relevant surface properties are the thermodynamic excess functions of a macroscopic slab, limited by the face of interest, in comparison with the bulk crystal. Strengths and weaknesses of the method used are discussed.