Adsorption of cysteine clusters on Au(110)−(1 × 1) surface: a DFT study

Abstract

Cysteine clusters of various sizes are investigated, as free structures and adsorbed on the Au(110)−(1 × 1) surface, by using density-functional theory. We analyse the adsorption of clusters in protonized and deprotonized forms. The presence of a trend for the values of bonding energy per adsorbed cysteine molecule as a function of cluster size is pointed out. To explain these findings we analyse the electronic density of states of the clusters and the charge transfer occurring between the surface and cysteine molecules. We emphasize the broadening of the molecular density of states as a function of cluster size. Details of the geometrical structure of the adsorbed clusters in protonized and deprotonized forms are compared and discussed from the perspective provided by the electronic structure calculation. By investigating the redistribution of the electron density upon the adsorption we point out the significant features of the molecule–surface charge transfer. In particular we show that the charge redistribution occurs only at the thiol end while the electronic density of the carboxylic group is not affected in the adsorbed state.