Metodi computazionali per la descrizione dei cristalli molecolari: strategie di utilizzo e sistemi modello

This present thesis work describes a first theoretical investigation on the molecular crystals of indigo and some alkyl derivatives 2,3-thieno(bis)imide (Cn-NT4N, with n = 1, 4, 5, 6 and 8) performed for prepare the ground for more in-depth studies on these systems and to test numerous methods of calculation. The first molecule is very rigid and have polymorphs that differ by packing at solid state while the Cn-NT4N family has different conformations that crystallize with different packings (conformational polymorphs). We used classical methods based on empirical potential modelsq, and quantum ab-initio methods, semi-empirical and based on the theory of functional densities. The various methods have been tested calculating the crystallographic structures and Raman spectra of the various polymorphs, also in order to support the interpretation of experimental results. The combinations of methods chosen in each case was carefully weighed on the features of the system under examination, on the purpose of the calculation, and on its cost. As we have heard in a conference: "a different horse for each race".