Electronic structure of the LL-cysteine dimers adsorbed on Au(111): a density functional theory study

The adsorption mechanisms of L- and LL-cysteine dimers on Au(111) surface was investigated by means of periodic density functional theory calculations. The computed binding energies suggest that LL dimer is stabilized by the interaction occurring between the COOH groups. Results for different molecular configurations show that for all the investigated adsorption geometries the L and LL molecules are physisorbed at a relatively high position with respect to the gold surface. By analysing the electronic structure of the adsorbate, we noted that upon the adsorption of LL dimer there is no competition between the mechanism of dimer formation and that of dimer adsorption on the gold surface. The calculated projected density of states allows us to locate the l-and LL-cysteine molecular orbitals with respect to the metal's Fermi level.