Electronic structure and chemical bonding of 3d-metal dimers ScX, X=Sc-Zn

The electronic and geometrical structures of the ground and excited states of the homonuclear Sc-2, mixed ScTi, ScV, ScCr, ScMn, ScFe, ScCo, ScNi, ScC u, and ScZn 3d-metal dimers and their anions have been calculated using the density functional theory with generalized gradient approximation for the exchange-correlation potential. The ground states of the neutral dimers are found to be (5)Sigma (-)(u) (Sc-2), (6)Sigma (+) (ScTi), (7)Sigma (+) (ScV ), (4)Sigma (+) (ScCr), (3)Sigma (+) (ScMn), (2)Delta (ScFe), (1)Sigma (+) (ScCo), (2)Sigma (+) (ScNi), (3)Delta (ScCu), and (4)Sigma (+) (ScZn). A na tural bond analysis reveals an antiferrimagnetic spin coupling in the groun d states of ScCr, ScMn, and ScFe. This is due to the electron transfer from Sc to the opposite atom and specific bond formations. While each dimer has a unique chemical bonding pattern, most curious is the localization of two 4s electrons at both atomic sites in the ground (5)Sigma (-)(u) state of S c-2, which leads to formation of two lone pairs and the bonding scheme: (3d + 3d)(alpha)(3)(4s + 4s)(beta)(1). No appreciable sd hybridization is foun d for the ground states of the ScX dimers except for ScNi. Even though the electron affinities of the ScX dimers are relatively low and do not exceed 1 eV, each ScX- (except ScCo-) possesses at least two states stable towards detachment of an extra electron. (C) 2001 American Institute of Physics.