Single Molecule Magnets form an ab initio point of view: from single molecules to the adsorption on surfaces

At present, the possibility to employ Single Molecule Magnets (SMMs) properties in real technological devices is still a challenge. In order to reach this target a significant extension of their spin life-time and a rational tuning of their properties on demand is mandatory. In this Ph.D. thesis a comprehensive theoretical and computational assessment of the main open questions related to the microscopic quantum origins of SMMs properties has been done together with the development of an ab initio protocol based on both DFT and post HF schemes able to describe SMMs electronic structure in any sort of chemical environment. The multi-spin origin of the ground state in polynuclear SMMs has been discussed and the several involved spin terms assessed. A fundamental extension of spin relaxation theory has been developed in order to account for the real complexity of the spin environment made by phonons and other SMMs spins. Spin relaxation phenomena have been addressed tracking down the origin of the spin-flip effective barrier reduction, observed experimentally and never interpreted before. The determination of the main contribution of molecular internal degrees of freedom at the origin of spin relaxation has also been pointed out for the first time, paving the ground for a rational design of molecular structures to extend relaxation time-scales. Finally, the issues related to the conservation of SMMs properties once adsorbed on a metallic substrate have also been addressed. A 2combination of different computational schemes made possible to highlight the striking importance of electronic and structural rearrangements of SMMs once deposited. This effect, largely underestimated in literature, has been observed both for what concerns substrate/SMM and SMM/SMM interactions, demonstrating, for instance, the possibility to modulate the molecular orientation playing with the SMMs organic scaffold degrees of freedom.