TABLE I: The geometries and adsorption energies for the structures of thioglycolic acid on Au(111) at 0.25ML. The entries θ , tilt direct and d$_{S}$$_{−}$$_{Au}$ refer to the polar angle between the normal vector of the surface and the S-C2 direction, the Au(111) surface region towards which the S-C2 is tilted, and the shortest Au-S bond length. The entries initial and optimized site stand for the S atom attachment site before and after optimization. The maximum adsorption energy is underlined. initial θ d$_{S}$$_{−}$$_{Au}$ optimized θ tilt d$_{S}$$_{−}$$_{Au}$ E$_{ads}$ site ˚ A site deg direct ˚ A eV bri 0 2.60 bri 2.9 hcp 2.97 0.27 45 2.60 bri-fcc 54.8 hcp 2.89 0.45 90 2.60 bri 86.9 hcp 3.16 0.47 fcc 0 2.60 bri-fcc 9.7 hcp 2.98 0.32 45 2.60 bri-fcc 61.0 hcp 3.11 0.36 90 2.60 top-fcc 83.7 hcp 3.18 0.50 hcp 0 2.60 bri-hcp 5.8 fcc 2.95 0.30 45 2.60 bri-hcp 54.2 fcc 2.87 0.48 90 2.60 hcp 89.4 fcc 3.58 0.44 top 0 2.60 top 8.0 hcp 2.93 0.26 45 2.60 top 54.8 hcp 2.81 0.37 90 2.60 top 74.2 fcc 2.57 0 . 63 tilted, and the shortest Au-S bond length, respectively. The entries initial and optimized site stand for the S atom attachment site before and after optimization. The columns 1-3 and 4-7 list structural data pertaining to the initial and the final optimized geometry. The maximum adsorption energy is underlined. Table I shows the adsorption energy for the most stable structure of the HSCH$_{2}$COOH on the Au(111) surface is 0.63 eV, and the adsorption site preferred by the sulfur atom is located at the atop site of the gold atom. This stable configuration is illustrated in Fig. 1a. The polar angle between the normal vector of the surface and the S-C2 direction is 74.2 ◦ . Fig. 1a indicates that at the low coverage, the HSCH$_{2}$COOH tends to lie down $^{8}$. The S-Au bond length is 2.57 ˚ A , which suggests that the bonding between the S atom in the 5