The first-principle technique is employed to determine the structure of the BP3S monomer, the structures of the molecular chains and monolayers on virtual Au（111), and the atomic structure of BP3S/Au（111) adsorption system. The results show that the BP3S monomer presents a symmetric structure, and the angle between two benzene rings is 3510. At first, many BP3S monomers are assembled into one stable molecular chain in the virtual Au（111), the distance between the neighbor monmers is 0.516 nm, and the bind energy between the monmer and the molecular chain is 0.071 eV. It is a self-assembly system. Then many molecular chains are assembled into two stable monolayers in the virtual Au（111)-(37) and Au（111)-(313), and their coverages are 0.20 ML and 0.14 ML, respectively. In the virtual Au（111)-(37) and Au（111)-(313), the angles between the molecular chains and the virtual surface are 60 and 30, respectively, and the binding energies between the monmer and two monolayers are 0.101 eV and 0.125 eV, respectively. They are both the self-assembly systems. Finally, two monolayers are adsorbed on the Au（111)-(37) and Au（111)-(313) at four adsorption sites. The S atom is easy to obtain two electrons and turn into S2- ion, and the Au atom is easy to lose one electron and become Au+ ion, so the bridge site（two Au+ ions) is more stable than the top site（one Au+ ion), while the hcp and fcc hollow sites（three Au+ ions) are both unstable. In the Au（111)-(37), the chemisorption energy of the bridge site（-1.879 eV) is lower than that of the top site（-1.511 eV). And in the Au（111)-(313), the chemisorption energy of the bridge site（-1.691 eV) is lower than that of the top site（-1.492 eV). The results are confirmed in the other S-Au adsorption systems, such as the C6H13S/Au（111). A comparison between the structures of the BP3S monolayer before and after being adsorbed on Au（111) clearly shows that the structural parameters of the adsorption system depend mainly on the interaction in the monolayer, and that the contribution of Au（111) to the structure of the monolayer is weak. These results are confirmed in the other self-assembly adsorption systems.
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