Electronic Structure of PassivatedAu38(SCH3)24Nanocrystal

Energetics, electronic structure, charging, and capacitive properties of bare and thiol-passivated ${\mathrm{Au}}_{38}$ gold nanocrystals were investigated via density-functional calculations. In the energy-optimized passivated nanocrystal, comprised of a truncated-octahedral face-centered-cubic ${\mathrm{Au}}_{38}$ core coated by a monolayer of 24 methylthiol $\left({\mathrm{SCH}}_3\right)$ 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.