V. CONCLUSION We have discussed the adsorption patterns of the HSCH$_{2}$COOH, SCH$_{2}$COOH, HSCH$_{2}$COO − , and SCH$_{2}$COO − molecules on the Au(111) substrate by first-principle the- oretical calculation. We have computed the partial density of states (PDOS) projected on the S and O2 atoms in the molecules on the Au(111) substrate, which display how the disso- ciation of the mercaptan hydrogen atom and the deprotonation of the carboxylic acid group affect the deposition and the corresponding electronic configuration. We have calculated the charge-density differences for the molecules on the Au(111) substrate, which illustrates various bonding characteristics. We have also studied the Raman vibrational spectra of the molecules adsorbed on the Au(111) substrate, and by the comparison of the experimental frequencies with the computational ones, we have identified which compounds and atomic displacements contribute to the frequencies. We have found the following adsorption mech- anism for the thioglycolic acid on the Au(111) surface. Upon the HSCH$_{2}$COOH molecules deposit on the Au(111), they can either remain intact, or turn into one of the following substances: 1) SCH$_{2}$COOH in the presence of the defect on the Au(111); 2) HSCH$_{2}$COO − by increasing pH value; 3) SCH$_{2}$COO − by the defect and increasing pH value. If the in- tact HSCH$_{2}$COOH is adsorbed on the gold substrate, the molecule lies down on the sur- face. When the SCH$_{2}$COOH molecules deposited on the Au(111) surface, some SCH$_{2}$COOH molecules lie on the substrate, but others rise up to a certain level. Thus, in the case of SCH$_{2}$COOH, different configurations may admix, and the molecules appear to be deposited on the gold substrate in a random fashion. If the carboxylic acid group in the HSCH$_{2}$COOH is deprotonated, the resulting HSCH$_{2}$COO − lies down on the surface. However, when the S-H bond in the HSCH$_{2}$COO − is broken and the molecule is turned into SCH$_{2}$COO − , it rises up to a certain level. 16