New Approach for the Correction of Ab initio Molecular Force Fields in Cartesian Coordinates

This paper presents a scaling technique applicable to Molecular force constants in Cartesian coordinates. In the Course of spectroscopic and structural research, it is a common practice to achieve better correspondence between measured and calculated vibrational frequencies of a molecule by appropriate scaling of the force constant matrices obtained by quantum chemical methods. However, the existing scaling procedure requires introduction of the complete system of internal coordinates, which may be tedious and time-consuming for complex molecules. Scaling scheme suggested in this paper is applied directly to Cartesian force constant matrices and thus does not require introduction of the internal coordinates. Practical implementation of the proposed approach is illustrated with the examples of simple molecules. The scheme allows imposing special constraints on the determined Cartesian scale factors, which may be used for obtaining scale factors possessing transferability properties. These properties are very important for vibrational spectra calculations of related Compounds, especially for large biological Molecules, associates and nanostructures. (C) 2008 Wiley Periodicals, Inc. Int J Quantum Chem 109: 28-33, 2009