title: Electrostatic properties of adsorbed polar molecules: opposite behavior of a single molecule and a molecular monolayer.
abstract: We compare the electrostatic behavior of a single polar molecule adsorbed on a solid substrate with that of an adsorbed polar monolayer. This is accomplished by comparing first principles calculations obtained within a cluster model and a periodic slab model, using benzene derivatives on the Si(111) surface as a representative test case. We find that the two models offer diametrically opposite descriptions of the surface electrostatic phenomena. Slab electrostatics is dominated by dipole reduction due to intermolecular dipole-dipole interactions that partially depolarize the molecules, with charge migration to the substrate playing a negligible role due to electric field suppression outside the monolayer. Conversely, cluster electrostatics is dominated by dipole enhancement due to charge migration to/from the substrate, with only a small polarization of the molecule. This establishes the important role played by long-range interactions, in addition to local chemical properties, in tailoring surface chemistry via polar molecule adsorption.
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel.
authors.forename: Dudi
authors.initials: D
authors.lastname: Deutsch
authors.forename: Amir
authors.initials: A
authors.lastname: Natan
authors.forename: Yoram
authors.initials: Y
authors.lastname: Shapira
authors.forename: Leeor
authors.initials: L
authors.lastname: Kronik