On the accuracy of density-functional methods for determining structures of dicationic binuclear ruthenocene derivatives bridged by an unsaturated molecule

Various exchange and correlation functionals have been examined in density-functional calculations for obtaining reliable optimized structures for dicationic binuclear ruthenocenes bridged by an unsaturated compound, which has a characteristic fulvene-type structure. First, we have performed extensive calculations for ruthenocene (RuCp2) in D5h symmetry. It has been found that the Ru-Cp optimized distance is linearly correlated with the energy difference between highest occupied a1′ and e2′ orbitals. We have then found that the optimized structure of dicationic binuclear ruthenocenes is strongly dependent of the a1′-e2′ orbital sequence observed in RuCp2. In particular, when exchange-correlation functionals giving the a1′