Lo sfruttamento completo della simmetria per i termini anarmonici della superficie di energia potenziale di molecole e solidi: implementazione nel codice Crystal

This thesis work has been carried out in the Theoretical chemistry group of the University of Torino, where Crystal , one of the most stable and reliable ab initio package for solid state simulations, has been developed for more than 40 years. The objective of these pages was to present the theoretical background and the implementation of a strategy to exploit symmetry in the evaluation of third- and fourth-order derivatives of the potential energy surface (PES), both in molecules and solids.