We live in a molecular world, almost closed shell in nature, and for this reason Chemistry has been a science dealing with closed shell mol- ecules. However, the high degree of experimental sophistication reached in the past decade has made more apparent the role of open shell structures in chemical research. A parallel phenomenon can be observed in the development of SCF theory, where closed shell molecular calculations at any level of complexity compose the main body of references which can be obtained in Quantum Chemistry today. Besides the linkage between experimental and theoretical...