Antiferromagnetic spin ordering in the dissociative adsorption of H_2 on Si(001): Density-functional calculations

摘要

The dissociative adsorption of an H_2 molecule on the Si(001) surface, which has been experimentally identified in terms of dissociation on one side of two adjacent Si dimers, is investigated by spin polarized density-functional calculations within the generalized-gradient approximation. In contrast to the prevailing nonmagnetic configuration of charge ordering, we propose a new ground state where the two single dangling bonds (DBs) created by H_2 dissociation are antiferromagnetically coupled with each other. Such a spin ordering is found to be energetically favored over the previously proposed charge ordering. In the latter configuration, the buckling of the two DBs amounts to a height difference (△h) of 0.63 A, caused by a Jahn–Teller-like distortion, while in the former configuration, their buckling is almost suppressed to be △h=0.03 A as a consequence of spin polarization.