Benzene adsorption on the Au(100)-3 x 3 surface has been studied with a periodical slab model by using the VAN functional. The results of geometry optimization indicate that the hollow site is energetically active for benzene adsorbed on the Au(100) surface. The two opposite carbon atoms are involved in the adsorption process, leading to a rehybridization of the two carbon atoms from sp(2) to sp(3) that makes the adsorbate state intermediate between benzene and 1,4-cyclohexadiene. The benzene adsorbed in the bridge and top positions is found to be energetically less favorable. The molecular orbital analysis also indicates the degenerate frontier molecular orbitals lose their degeneracy with a decrease in symmetry. The two carbon atoms in the opposite positions are bonded to the neighboring Au atoms with di-sigma bonds. (c) 2005 Elsevier B.V. All rights reserved.