FIG. 1: (a) The thioglycolic acid (HSCH$_{2}$COOH) on the Au(111) surface. (b) SCH$_{2}$COOH on the surface. (c) HSCH$_{2}$COO − on the surface. (d) SCH$_{2}$COO − on the surface. HSCH$_{2}$COOH and the gold atom could be described as chemisorption $^{11}$. B. The SCH$_{2}$COOH molecule on the gold substrate Ruan et al. used 2,2’-dithiodiacetic acid to make SAMs on the gold surface $^{9}$, then the SCH$_{2}$COOH is deposited on the surface. The SCH$_{2}$COOH can also be obtained from the HSCH$_{2}$COOH molecule by taking away the mercaptan hydrogen atom which is initially attached to the sulfur. The adsorption pattern of the SCH$_{2}$COOH molecule on the Au(111) surface is depicted in Table II. The adsorption energy for the most stable configuration of the SCH$_{2}$COOH on the Au(111) surface in Table II is 2.34 eV, and the favored adsorption site by the sulfur atom is in the hcp hollow center, but leaned to the Au-Au bridge. The corresponding structure is shown in Fig. 1b. The sulfur atom forms bonds with two Au atoms, and the S-Au bond length is 2.47 ˚ A . The angle between the normal vector of the surface and the S-C2 direction is 68.0 ◦ . However, in Table II there are two configurations marked by # (bri-45 ◦ and hcp-45 ◦ ) with adsorption energies 2.33 eV, which is close to the energy of the most stable one (2.34 eV). The corresponding angles θ for these two # 6