Scaling factors for the prediction of the frequencies of the ring modes inbenzene derivatives

The performance of semiempirical, ab initio, and density functional methods in calculating and describing the vibrational frequencies of benzene and s everal derivatives was determined. Different levels were used. The normal m odes of the ring were characterized by the magnitude and direction of the d isplacement vector. Two new procedures of scaling the frequencies were pres ented. Scaling factors were determined at different levels. A significant r eduction in the predicted frequencies of the ring modes of several benzene derivatives was obtained over the one-factor overall scaling procedure.