Anharmonicity effects on the structural and vibrational properties of molecular systems in different electronic states

The research work of Marco Mendolicchio involves the inclusion of anharmonicity effects in the calculation of structural and vibrational properties. The thesis is divided into two main parts: the first deals with the development of an algorithmic for the calculation of anharmonic force fields in normal coordinates, that in turn allow anharmonic vibrational frequencies to be derived through the vibrational second-order perturbation theory (VPT2). The second part involves the implementation of a standalone code for the fitting of accurate equilibrium molecular structures by means of the semi-experimental approach.