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Byline: Sudip Chakraborty, S.V. Ghaisas, Chiranjib Majumder We report an extensive first-principles investigation of the structure and electronic properties of small Si n (n = 1, 2, 3, 4, and 6) clusters deposited on the Au(111) surface. The calculations were performed using a plane wave based pseudopotential method under the framework of density functional theory. The electron-ion interaction energy has been described using ultrasoft pseudopotentials (USPP) and the spin polarised GGA scheme was used for the exchange correlation energy. The results reveal that Si atom prefers to adsorb on the hcp site of the Au(111) surface with strong binding energy. For Si3, the closed triangle geometry of the bare cluster forms an open triangle by rupturing one of the three Si-Si bonds. Remarkable structural changes in the gas phase geometries were observed from Si4 onwards. For example, while the adsorption of rhombus in parallel and perpendicular orientation to the surface plane remains almost unaltered, the tetrahedral conformation becomes almost flat by the interaction of Au surface. The nature of chemical bonding between Au surface and Si clusters was investigated from the charge distribution analysis and the electronic density of states (EDOS). Based on charge distribution analysis it is found that Si atoms transfer charges to the Au surface. Based on the results it is inferred that Si clusters deposition on the Au surface involves large energy release and would lead to coat the surface by spill over of Si atoms rather than island formation.

Theoretical computations conducted to understand the geometric and electronic features of the 4-nitro-2,5-bis(4-mercaptophenylethynyl)phenlyamine molecule are presented. The electronic transport pattern in this molecule is analyzed from the electronic structure and spatial orientations of the molecular orbitals.