Headgroup dimerization in methanethiol monolayers on the Au(111) surface: a density functional theory study

A long-standing controversy related to the dimer pattern formed by S atoms in methanethiol ($CH_{3}SH$) on the Au(111) surface has been resolved using density functional theory. For the first time, dimerization of methanethiol adsorbates on the Au(111) surface is established by computational modeling. For methylthiolate ($CH_{3}S$), it is shown that the S atoms do not dimerize at high coverage but reveal a dimer pattern at intermediate coverage. Molecular dynamics simulation at high coverage demonstrates that the observed dialkyl disulfide species are formed during the desorption process, and thus are not attached to the surface.