Electronic Structure of Passivated Au 38 s SCH 3 d 24 Nanocrystal

Energetics, electronic structure, charging, and capacitive properties of bare and thiol-passivated Au38 gold nanocrystals were investigated via density-functional calculations. In the energy-optimized passivated nanocrystal, comprised of a truncated-octahedral face-centered-cubic Au38 core coated by a monolayer of 24 methylthiol sSCH3d molecules, we find interfacial charge transfer of about 2e from the outermost gold atoms to the sulfur atoms. The estimated effective capacitance is 0.084 aF, correlating well with recent electrochemical measurements. Charging takes place within the molecular layer. Molecular adsorption of dimethyl-disulfide is found to be energetically unfavorable for a gold cluster of this size. [S0031-9007(99)08937-1]