The electronic and structural properties of the self-assembled monolayer of Au-benzene-1,4-dithiol-Au molecules*

The electronic and structural properties of the self-assembled monolayer of Au-benzene-1,4-dithiol-Au molecules are calculated by first-principles calculation methods. The Au-S bond length obtained is 2.20{\AA}, which is about 6.8{\%} smaller than the sum of their covalent radii of 2.36 {\AA}. The Au-S-C bond angle obtained is 98.9$^{0}$, which is within the range of known bond angles of S, e.g. $\angle $FSF=98.2$^{0}$ for$^{ }$SF$_{2}$, $\angle $ClSCl =103$^{0 }$for SCl$_{2}$ and $\angle $CSH =96.4$^{0 }$for CH$_{3}$CH$_{5}$-SH. The Au 5d band is dominantly located at -2.3 eV below the Fermi level, E$_{F}$, with a sharp peak in the partial density of states (PDOS). The PDOS's also show that the highest-occupied-molecular-orbital band contains S 3p, C 2p and Au 5d hybridized states, while the lowest-unoccupied-molecular-orbital band contains S 3p, C 2p, Au 6s and Au 5d hybridized states. The dominant Au 6s states are located at about -1.5eV and 1.3eV relative to E$_{F}$. The present result shows that Au 5d states, which are usually ignored in previous theoretical studies, play an important role in the S-Au bonding and contribute significantly to the transport property of the molecule.