Comparison study of the prediction of Raman intensities using electronic structure methods

Raman intensities have been computed for a series of test molecules (N-2, H2S, H2O, H2CO, CH4, C2H2, C2H4, C2H6, SiO2, NH3, CH2F2, and CH2Cl2) using Hartree-Fock, second-order Moller-Plesset perturbation theory (MP2), and density functional theory, including local, gradient-corrected, and hybrid methods (S-VWN, B-LYP and B3-LYP, and MPW1-PW91) to evaluate their relative performance. Comparisons were made with three different basis sets: 6-31G(d), Sadlej, and aug-cc-pVTZ. The quality of basis set used was found to be the most important factor in achieving quantitative results. The medium sized Sadlej basis provided excellent quantitative Raman intensities, comparable to those obtained with the much larger aug-cc-pVTZ basis set. Harmonic vibrational frequencies computed with the Sadlej basis set were in good agreement with experimental fundamentals. For the quantitative prediction of vibrational Raman spectra, the Sadlej basis set is an excellent compromise between computational cost and quality of results. (C) 1999 American Institute of Physics. [S0021-9606(99)30543-2].