VIBRATIONAL FREQUENCIES OF A1F(3) - AN AB-INITIO MO STUDY EVALUATING DIFFERENT METHODS ON A TRICKY CASE

The vibrational frequencies of AlF3 have been calculated with ah initi o methods at the Hartree-Fock level, at correlated levels (MP2, QCISD, MCSCF) and with the LDF method including local (LSD) and non-local sp in density (NLSD) functions. The basis set sensitivity was examined wi th a large number of basis sets including polarization and diffuse fun ctions. The calculations do not confirm the assignment of nu(4) to 263 cm(-1), but suggest a frequency of approximate to 240 cm(-1) for this mode. The nu(1) mode most probably is close to 670-675 cm(-1). The lo west recommendable level for vibrational analysis of AlF3, and probabl y also for related species, seems to be HF/6-31+G.