Raman and infrared vibrational frequencies and elastic properties of solid BaFCl calculated with various Hamiltonians:: an ab initio study

The structural, elastic, vibrational and electronic properties of barium fluorochloride (BaFCl) have been investigated for the first time at the ab initio level, by using the periodic CRYSTAL program. Both Hartree-Fock (HF) and density functional theory (DFT) Hamiltonians have been used. with the latter in its local density (LV), gradient-corrected (PP), and hybrid (B3LYP) versions. All properties, and in particular the phonon frequencies and the elastic constants, are strongly Hamiltonian dependent. The structural features are in reasonable agreement with experiment, the percentage deviation being smaller than 5%, in all cases. The B3LYP elastic constants are in good agreement with experiment, whereas LV systematically overestimates them. PP and B3LYP provide the best results for the vibrational frequencies. the mean percentage absolute difference with respect to experiment being 2.9 and 4.3% for Raman and 4.8 and 6.3%. for infrared mode frequencies. respectively.