Structure of the methylthiolate monolayer on Ag (1Â 1Â 1): The role of substrate vacancies

► Substrate reconstruction strongly stabilizes the monolayer of SCH3 on Ag (1 1 1). ► The most stable structure involves a reduced density (5/7) of top-most layer Ag atoms. ► The adsorption pattern consists in Ag3S3 units surrounded by hexagons of Ag atoms. ► This model explains the small rumpling of the monolayer observed in experiments.