title: Dipole orientation and surface cluster size effects on chemisorption-induced magnetism: a DFT study of the interaction of gold-thiopolypeptide.
abstract: A nanosystem formed by a high electric dipole moment thiopolypeptide alpha-helix, consisting of eight l-glycine units, chemisorbed on the (111) surface of Au23 and Au55 clusters, with the S as the linking atom, was studied using the wave function broken symmetry UDFT method. We have found a strong correlation between the orientation of the electric dipole of the alpha-helix and charge transfer and the magnetic behavior of the adsorbate-cluster system. Upon chemisorption, dipole moments may be quenched or enhanced, with respect to the gas phase value, with the strongest reduction corresponding to the magnetic state. A reduction of the alpha-helix's electric dipole with the net charge transfer from the Au surface was obtained for the more stable state. In this state description, it may happen that the calculated spin densities of the chemisorbed alpha-helix and its free radical form are similar. The magnetic properties are strongly dependent on the size of the Au cluster and on its electronic structure with respect to nuclei positions. In general, the localized spin density per atom increases and the magnetization of the extended system decreases with cluster size, a trend found experimentally for organic monolayers with a similar type of adsorbate we consider here.
authors.affiliation: Departamento de Química, FACYT, Universidad de Carabobo, Apartado 2005, Valencia, Edo. Carabobo, Venezuela. lpuerta@uc.edu.ve
authors.forename: Luis
authors.initials: L
authors.lastname: Puerta
authors.forename: Héctor J
authors.initials: HJ
authors.lastname: Franco
authors.forename: Juan
authors.initials: J
authors.lastname: Murgich
authors.forename: Carlos
authors.initials: C
authors.lastname: Gonzalez
authors.forename: Yamil
authors.initials: Y
authors.lastname: Simón-Manso
authors.forename: Vladimiro
authors.initials: V
authors.lastname: Mujica
mesh_terms: D000327:Adsorption; D006046:Gold / Q000737:chemistry*; D008280:Magnetics; D010455:Peptides / Q000737:chemistry*; D011789:Quantum Theory; D013455:Sulfur / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D010455:Peptides; D013455:Sulfur; D006046:Gold