Scaling factors for the prediction of vibrational spectra. I. Benzene molecule

The performance of semiempirical, ab initio, and density functional methods in calculating and describing the vibrational frequencies of benzene was determined. Different levels were used. The modes were characterized by the magnitude and direction of the displacement vector. The error in the calculated frequencies was reduced using two procedures to obtain the scaled frequencies. Scaling equations were determined for each theoretical method. Specific scale factors were calculated to reduce the error in the ring modes of benzene derivatives.