The spin properties of a system are typically characterized by the spin density. However, there are singlet systems such as diradicals, antiferromagnets or transition metal complexes for which the spin density is clearly not enough to characterize the physical situation (particularly if they are properly described with multireference wave functions). Indeed, it is often assumed the existence of localized spins, even though the spin density vanishes in every point of the space. We have most recently derived a new general formulation for the decomposition of <S2> into atomic and diatomic contributions that fulfills all necessary physical requirements imposed to date, and this applies to both single- and multideterminant wave functions.The analysis of the atomic and diatomic contributions to the total <S2> is called local spin analysis.We will also present the application of the local spin analysis to characterize and quantify the polyradical character of molecular systems.The behavior of several indices for diradical character is tested for a simple model diradical. The advantages of using descriptors derived from the local spin analysis is illustrated with more involved examples including complex dissociation profiles and prototypical diradical systems such as trimethylenethane. A model triradical system is also studied in detail and the local spin analysis is used to distinguish several patterns of spin distributions that can be found for different electronic states. How close a real molecular system is to an ideal system of k perfectly localized spin centers is utilized to define a measure of its k-radical character. The spin properties and triradical character of the lowest-lying electronic states of a number of all s, all p and s�p organic triradicals will be discussed in detail.E. Ramos-Cordoba, E. Matito, I. Mayer, P. Salvador J. Chem. Theory Comput. 2012 , 8, 1270.E. Ramos-Cordoba, E. Matito, P. Salvador, I. Mayer Phys. Chem. Chem. Phys 2012 , 14, 15291�15298.E. Ramos-Cordoba, P. Salvador, M. Reiher Chem. Eur. J. 2013 , 19, 15267�15275.E. Ramos-Cordoba, P. Salvador, J. Chem. Theory Comput. 2014  , 10, 634-641.

Recent advances in local spin analysis: Quantification and characterization of polyradical character

248th National Meeting (2014)

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