Local spin analysis and chemical bonding

The electronic structure of main-group diatomic molecules is discussed in the light of local spin analysis. A deep investigation into the origin of local spins and their coupling is presented. It is shown that the presence of significant local spins in bonded molecules flags deviations from the classical bonding prototypes. For the notorious example of the C2 molecule, the local spin analysis indicates that its ground state has all ingredients to be categorized as a diradical. Is C2 a diradical? Local spin analysis is used to discuss the electronic structure of main-group diatomic molecules. The presence of significant local spins in bonded molecules flags deviations from the classical bonding prototypes, that is, the extent of local spin is a measure of the deviation of a bond from perfect covalent character (see figure). The results indicate that the C2 molecule in its ground state has all the ingredients to be categorized as a diradicalFinancial help has been furnished by the Spanish MICINN Projects No. CTQ2011-23441/BQU and CTQ2011-23156/BQU. Financial support from MICINN and the FEDER fund (European Fund for Regional Development) was also provided by grant UNGI08-4E-003. Financial support from the Generalitat de Catalunya (SGR528 and Xarxa de Referencia en Quimica Teorica i Computacional) is also acknowledged. E. R-C. acknowledges support from the Spanish FPU program (Grant No. AP2008-01231). M. R. is grateful to ETH Zurich and the Swiss National Science Foundation (SNF) for financial suppor