A new, reduced set of scaling factors for both SQM and ESFF calculations

Scaling methods are often used to facilitate the computational prediction and interpretation of vibrational spectra calculated on the basis of quadratic force fields. In this work, a new, reduced set of scaling factors is proposed for both scaled quantum mechanical (SQM) force fields and the recently proposed effective scaling frequency factor (ESFF) method. The calculations are based on a training set of 30 molecules (660 experimental frequencies). By an appropriate regrouping of internal coordinates we were able to reduce the number of scaling factors from 11 down to 9 without loss of quality in the scaled frequencies. The main difference between the new and previously used set of scaling factors is the splitting of the general non-hydrogen XX stretch into two subgroups that differ in their scaling factors by nearly 0.02. This increases flexibility in the 1000–2500 cm−1 region.