We have studied the adsorption structures of methylthiolate (MeS) on the Au (111) surface using density functional theory. The most stable adsorption structure of MeS is the MeS–Au–MeS configuration, which has been proposed by Maksymovych and co-workers (2006 Phys. Rev. Lett. 97 146103), followed by the bridge configuration. The calculated work function change and vibrational mode analysis for the two configurations agree quite well with the experimental results. These results strongly support the conclusion that the MeS–Au–MeS and the bridge configurations coexist on the MeS adsorbed Au (111) surface.