Evaluation of MP2, DFT, and DFT-D methods for the prediction of infrared spectra of peptides.

The prediction accuracy of second-order Moller-Plesset theory MP2 and density functional theory DFT-(D) with and without empirical dispersion correction within the resolution of identity approximation (ri) have been investigated for the assignment of infrared spectra of gas-phase peptides. A training set of 17 conformers of phenylalanine containing capped peptides have been used to establish mode-specific local scaling factors. Inclusion of dispersion terms at the DFT level turns to significantly improve the accuracy of predicted IR spectra.

Transferable specific scaling factors for interpretation of infrared spectra of biomolecules from density functional theory.

A set of transferable local scaling factors is established for assignment of infrared spectra of molecular systems of biological interest experimentally recorded under gas-phase conditions. Each scaling factor is specific for an experimentally observable vibrational mode chosen among those bringing significant structural information. Those factors are provided for harmonic calculations at the DFT B3LYP and DFT B3PW91 levels respectively with 7 and 2 different basis sets.