content_image/340564.jpg
<img src='content_image/340564.jpg'>

angle θ for top-45 ◦ structure (the # marked configuration) is 51.8 ◦ . The stable structures in Table IV indicate that when the SCH$_{2}$COO − is deposited on the Au(111) surface, the molecule rises up to a certain level 8 (see Fig. 1d). 

## E. Electronic Structures 

To understand how the dissociation of the mercaptan-hydrogen atom and the deproto- nation of the carboxylic acid group play roles in the adsorption process, we calculate the partial density of states (PDOS) projected on the S and O2 atoms in the HSCH$_{2}$COOH, SCH$_{2}$COOH, HSCH$_{2}$COO − , SCH$_{2}$COO − molecule deposited on the Au(111) substrate. There are three sharp peaks in the PDOS projected on the S atom in the isolated HSCH$_{2}$COOH molecule (Fig. 2a). The major contributions of three peaks come from π , σ and π ∗ orbitals in the S-C bond. To calibrate the Fermi level for the isolated molecule, 

