A FLEXIBLE METHOD FOR CALCULATING VIBRATIONAL-SPECTRA OF CLUSTERS APPLIED TO METHANOL

A method is presented for calculating vibrational spectra of clusters using intra-and intermolecular potential models of different origin. T he two types of potentials are tuned and coupled to construct a total cluster potential. The determination of minima on this cluster potenti al energy surface, and the expansion of the potential about the minimu m configurations makes it possible to apply standard spectroscopic met hods. Starting from a normal mode analysis, harmonic and anharmonic fr equency shifts are calculated using perturbational and variational met hods for methanol clusters from the dimer to the hexamer. The results using the empirical OPLS potential model are compared with each other, with the harmonic line shift calculations for a calculated potential in the SCF approximation, and with the experimental data. There is an improvement with respect to the results obtained so far, however, the need for a better description of the intermolecular potential is point ed out.