An effective scaling frequency factor method for scaling of harmonic vibrational frequencies: Application to toluene, styrene and its 4-methyl derivative

The predictive capabilities of the newly proposed effective scaling frequency factor (ESFF) method and transferability of scaling factors are checked. A set of three related but with different structural motifs molecules, i.e. toluene, styrene and 4-methylstyrene, was used. Four sets of optimized local scaling factors were generated on the basis of different choices of bands from the experimental IR spectra. In all cases the spectral range was 3000-400 cm−1. The best fitting was obtained with the so-called Set A (66 experimental bands and 14 optimized local scaling factors). Only slightly worse results were obtained with the Set B containing merely eight local scaling factors. Different statistical tests demonstrate good transferability of local scaling factors as well as better performance of the ESFF approach than Pulay's SQM method. In particular, the RMS deviation calculated for 66 vibrational modes with ESFF is 28% lower than that obtained with SQM method.