GLYPH<s45>GLYPH<s56> GLYPH<s45>GLYPH<s54> GLYPH<s45>GLYPH<s52> GLYPH<s45>GLYPH<s50> GLYPH<s48> GLYPH<s50> GLYPH<s52> GLYPH<s54> GLYPH<s48> GLYPH<s50>GLYPH<s48> GLYPH<s52>GLYPH<s48> GLYPH<s54>GLYPH<s48> GLYPH<s56>GLYPH<s48> GLYPH<s49>GLYPH<s48>GLYPH<s48> GLYPH<s49>GLYPH<s50>GLYPH<s48> GLYPH<s40>GLYPH<s99>GLYPH<s41> GLYPH<s80>GLYPH<s68>GLYPH<s79> GLYPH<s83>GLYPH<s32> GLYPH<s112>GLYPH<s114> GLYPH<s111>GLYPH<s106>GLYPH<s101>GLYPH<s99>GLYPH<s116> GLYPH<s101>GLYPH<s100>GLYPH<s32> GLYPH<s111>GLYPH<s110>GLYPH<s32> GLYPH<s65>GLYPH<s117>GLYPH<s40> GLYPH<s49>GLYPH<s49>GLYPH<s49>GLYPH<s41> GLYPH<s69>GLYPH<s45>GLYPH<s69> GLYPH<s70> GLYPH<s65>GLYPH<s117>GLYPH<s40>GLYPH<s49>GLYPH<s49>GLYPH<s49>GLYPH<s41> GLYPH<s45>GLYPH<s56> GLYPH<s45>GLYPH<s54> GLYPH<s45>GLYPH<s52> GLYPH<s45>GLYPH<s50> GLYPH<s48> GLYPH<s50> GLYPH<s52> GLYPH<s54> GLYPH<s48>GLYPH<s46>GLYPH<s53> GLYPH<s49>GLYPH<s46>GLYPH<s48> GLYPH<s49>GLYPH<s46>GLYPH<s53> GLYPH<s50>GLYPH<s46>GLYPH<s48> GLYPH<s40>GLYPH<s98>GLYPH<s41> GLYPH<s80>GLYPH<s68>GLYPH<s79> GLYPH<s83>GLYPH<s32> GLYPH<s112>GLYPH<s114> GLYPH<s111>GLYPH<s106>GLYPH<s101>GLYPH<s99>GLYPH<s116> GLYPH<s101>GLYPH<s100>GLYPH<s32> GLYPH<s111>GLYPH<s110>GLYPH<s32> GLYPH<s116> GLYPH<s104>GLYPH<s101>GLYPH<s32> GLYPH<s79> GLYPH<s50>GLYPH<s32> GLYPH<s97>GLYPH<s116> GLYPH<s111>GLYPH<s109> GLYPH<s69>GLYPH<s45>GLYPH<s69> GLYPH<s70> GLYPH<s72>GLYPH<s83>GLYPH<s67>GLYPH<s72>GLYPH<s50>GLYPH<s67>GLYPH<s79>GLYPH<s79>GLYPH<s72> GLYPH<s32> GLYPH<s49> GLYPH<s50> GLYPH<s51> GLYPH<s52> GLYPH<s53> GLYPH<s54> GLYPH<s55> GLYPH<s56> GLYPH<s57> GLYPH<s45>GLYPH<s56> GLYPH<s45>GLYPH<s54> GLYPH<s45>GLYPH<s52> GLYPH<s45>GLYPH<s50> GLYPH<s48> GLYPH<s50> GLYPH<s52> GLYPH<s54> GLYPH<s49> GLYPH<s50> GLYPH<s51> GLYPH<s52> GLYPH<s53> GLYPH<s54> GLYPH<s55> GLYPH<s42> GLYPH<s40>GLYPH<s97>GLYPH<s41> GLYPH<s80>GLYPH<s68>GLYPH<s79> GLYPH<s83>GLYPH<s32> GLYPH<s112>GLYPH<s114> GLYPH<s111>GLYPH<s106>GLYPH<s101>GLYPH<s99>GLYPH<s116> GLYPH<s101>GLYPH<s100>GLYPH<s32> GLYPH<s111>GLYPH<s110>GLYPH<s32> GLYPH<s116> GLYPH<s104>GLYPH<s101>GLYPH<s32> GLYPH<s83>GLYPH<s32> GLYPH<s97>GLYPH<s116> GLYPH<s111>GLYPH<s109> GLYPH<s69>GLYPH<s45>GLYPH<s69> GLYPH<s70> GLYPH<s32> GLYPH<s72>GLYPH<s83>GLYPH<s67>GLYPH<s72>GLYPH<s50>GLYPH<s67>GLYPH<s79>GLYPH<s79>GLYPH<s72> FIG. 2: (a)-(b) PDOS projected on the S and O2 atom in the isolated HSCH$_{2}$COOH, (c) DOS for a pure Au(111) surface. in the calculation we have seperated the HSCH$_{2}$COOH molecule from the gold surface by 8 ˚ A so that there is no interaction between the molecule and the substrate. The correspond- ing PDOS projected on the S atom can be regarded as that in the isolated HSCH$_{2}$COOH molecule. The density of states for the pure gold surface vanishes above 6eV (Fig. 2c). The π ∗ orbital is located on the right edge of the Au d band, the π orbital is near the left edge of the Au d band, whereas the σ orbital overlaps with the gold d band (Fig. 2a, Fig. 2c). Upon the HSCH$_{2}$COOH molecule is deposited on the surface (Fig. 3a), the σ and π ∗ states disperse as a consequence of the mixing with the gold d states, whereas π orbital remains sharp and shifts toward more negative energy. The adsorption energy of 0.63eV indicates that the major interaction between the sulfur in the HSCH$_{2}$COOH molecule and the gold surface is not van der Waals force, so Fig. 3a might not have the signature of the weak bond. If the mercaptan-hydrogen atom is dissociated from the S atom, the π state splits indicat- ing a stronger S-Au bonding interaction originating from the hybridization of the π orbital of the SCH$_{2}$COOH with the gold d band (Fig. 3b). The PDOS projected on the S atom is insensitive to the deprotonation of the carboxylic acid group, which explains why the profiles of Fig. 3a and Fig. 3c are similar so are Fig. 3b and Fig. 3d. No energy gap in the PDOS projected on the S atom attached to the Au(111) surface (Fig. 3a-3d). This is because the HOMO and LUMO level of the S atom fall into the energy range of the gold d-band with a concomitant hybridization, that is, the PDOS projected on the S atom near the Fermi level is dominated by d-states from the Au(111) surface. The effect of the deprotonation of the carboxylic acid group is demonstrated by the PDOS projected on the O2 atom (Fig. 10