The adsorption structures of benzenethiol molecules on the Au(1 1 1) surface are investigated by using ab initio total-energy calculations. At low coverage, the molecule is adsorbed at the bridge site slightly shifted towards the fcc-hollow site, and is significantly tilted from the surface normal. The adsorption of benzenethiolates induces a repulsive interaction between surface Au atoms, which has large contribution to the stability of the adsorption state. At high coverage, which corresponds to the SAM structures, the molecules form the (2root3 x root3)R30degrees herringbone structure. They are also adsorbed at the bridge sites, as in the low coverage case, but the tilting angles are very small due to the steric hindrance. (C) 2004 Elsevier B.V. All rights reserved.