  The responsive behavior of methanethiol and methylthiolate molecules on the
Au(111) surface with an applied electrical potential is studied, and it is
shown how the sulfur adsorption site, the S-H bond orientation and the
interacting energy change with an external electric field strength. The
electron charge density corresponding to an electric field minus that obtained
in zero field, with zero-field optimal geometry, is calculated to explain the
responsive behavior. The interacting energy for the intact methanethiol
adsorption is larger than that for the dissociative one, showing that an
external electric field can not make the hydrogen dissociate from the sulfur.
