Dual Basis Approach for Ab Initio Anharmonic Calculations of Vibrational Spectroscopy: Application to Micro-Solvated Biomolecules.

Roy, Tapta Kanchan; Gerber, R Benny

A dual electronic basis set approach is introduced for more efficient but accurate calculations of the anharmonic vibrational spectra in the framework of vibrational self-consistent field (VSCF) theory. In this approach, an accurate basis set is used to compute the vibrational spectra at the harmonic level. The results are used to scale the potential surface from a more modest but much more efficient basis set. The scaling is such that at the harmonic level the new, scaled potential agrees with the one of the accurate basis set. The approach is tested in application of the micro-solvated, protected amino acid Ac-Phe-OMe , by using the scaled anharmonic hybrid potential in the VSCF and VSCF-PT2 algorithms. The hybrid potential method yields results in good accord with experiment, and very close to these obtained in calculations with the high level, very costly potential from the large basis set. At the same time, the hybrid potential calculations are much less expensive. The results of the hybrid calculations are much more accurate than these computed from the potential surface corresponding to the modest basis set. The results are very encouraging for using the hybrid potential method for inexpensive yet sufficiently accurate anharmonic calculations for the spectra of large bio-molecules.