IMPLEMENTATION OF SEMICLASSICAL THEORIES FOR SPECTROSCOPY

Vibrational spectroscopy is a fundamental tool for detecting and understanding the structure of molecular systems. Alongside the experimental measures, theoretical methods have been always employed to interpret and understand vibrational spectra. The semiclassical approach has demonstrated its reliability in the field, especially by means of the recent “Multiple Coherent” and “Divide and Conquer” formulations. In this PhD thesis the implementation and application of these modern techniques to a variety of molecular systems are presented, ranging from isolated medium size molecules to complex supramolecular systems, up to more than one hundred degrees of freedom. In particular the vibrational features of glycine, deoxyguanosine, a small dipeptide and glycine-based supramolecular systems are illustrated and discussed. A final Section is dedicated to the possibility to employ the Amber94 classical molecular force field, for computationally cheaper semiclassical calculations. This work demonstrates and highlights the validity and accuracy of semiclassical methods as theoretical spectroscopicy tools by successfully detecting quantum effects in medium size systems, whereas other formulations fail.