ABSTRACT
There has been intense interest in the pursuit of new computational methods for the calculation of vibrational anharmonic spectra in order to characterize and assign the observed bands of high resolution IR and Raman spectra often obtained with great success through very sophisticated experiments. This theoretical approach requires, in general, two restricting steps: the construction of the potential energy surface and the solution of the vibrational equation in order to obtain the anharmonic energy levels. For the potential energy surface, the determination of the potential function is based on electronic energy data calculated by sophisticated post-Hartree-Fock methods, as CCSD(T), in a grid in which the required number of points grows drastically with increasing molecule size. The solution to the vibrational equation is based on perturbational, variational or variation-perturbational methods. The selection of method usually depends on the nature of the problem and the vibrational levels (fundamental bands, harmonics, combinations) of interest.
