Uniform versus Nonuniform Scaling of Normal Modes Predicted by Ab Initio Calculations: A Test on 2-(2,6-Dichlorophenyl)-N-(1,3-thiazol-2yl) Acetamide

Abstract

A test on calculated vibrational modes of 2-(2,6-dichlorophenyl)-N-(1,3-thiazol-2yl) acetamide using ab initio density functional method has been performed. The calculated harmonic vibrational frequencies are scaled via two schemes, uniform, νscaled=0.9648νcalculated, and nonuniform, νscaled=22.1+0.9543νcalculated. Scaled vibrational modes are compared with experimental FTIR bands. A good correlation is shown between scaled frequencies with the correlation coefficient, R2=0.99638-0.99639. This clearly shows that both schemes efficiently reproduce observed spectrum. However, a close investigation of individual normal modes reveals that nonuniform scaling performs much better than uniform scaling especially in the high frequency region.

Structural, Vibrational and Electronic Properties of cis and trans Conformers of 4-Hydroxy-l-Proline: A Density Functional Approach

“…Initial geometries of cis-and trans-4HLYP are fully optimized without any symmetry constraint in the potential energy surfaces (PESs) using gradient corrected hybrid functional B3LYP [9, 10] and 6-31+G(d,p) basis set. B3LYP is one of the most widely used functionals in case of medium size biomolecules and hence, employed successfully in a number of previous studies [7,[11][12][13][14]. Vibrational frequency calculations are repeated using optimized geometries at the same level of theory.…”