AN ABINITIO STUDY OF THE EQUILIBRIUM GEOMETRIES AND VIBRATIONAL FREQUENCIES OF THE GROUP-IIA DIFLUORIDES BEF2,MGF2,CAF2

Ab initio molecular orbital calculations have been performed on the ground electronic states of BeF2, MgF2 and CaF2. Minimum energy geometries and vibrational frequencies were calculated at the Hartree-Fock (HF) level using analytical derivative methods. Some account was taken of electron correlation by performing the geometry optimizations at the Møller-Plesset second-order (MP2) level; vibrational frequencies were also calculated at this level. BeF2 and MgF2 were found to have linear, D∞h equilibrium geometries, whereas CaF2 was found to have a C2v geometry, with a bond angle of 152°. A single-point configuration interaction calculation including single and double excitations (CISD) was performed at the MP2 optimized geometry to gain some insight into the factors which determine the equilibrium geometry of CaF2. © 1990.