Theoretical studies on vibrational spectra of some aluminum halides: Effect of theoretical methods and basis sets

The vibrational spectra of aluminum halides, AlX3 (X = F, Cl, Br and I) and their dimers, Al2X6, have been systematically investigated by ab initio restricted Hartree-Fock (RHF) and density functional B3LYP and B3P86 methods with LanL2DZ, SDD, CEP-31G and DGDZVP basis sets. The optimized geometries, calculated vibrational frequencies were evaluated via comparing with the experimental data. The vibrational frequencies, calculated by these methods with different basis sets, were compared to each other. The effect of the methods and the basis sets used on the calculated vibrational frequencies was discussed. The best fittings values between the calculated and the measured vibrational frequencies were achieved by B3LYP/DGDZVP theoretical level, with this method, the deviations are less than 2% for Al-X stretching vibrational modes in AlX3 and less than 4% for Al-X stretching vibrational modes in Al2X6. Some vibrational frequencies of Al(III) halides were predicted.