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Structural properties of 4-bromostyrene (Br-Sty) on the Si(001)-(1x2) surface are investigated by ab initio calculation based on density functional theory. For the adsorption of Br-Sty molecule on Si(001)-(1x2), we have assumed binding on the clean Si surface and binding on the partially-hydrogen passivated Si surface. For the clean Si surface, we have proposed three possible binding sides: (i) Br-terminated (Model I), (ii) C-terminated (Model II), and (iii) ring-shaped binding (Model III). Adsorption energies of these models have been found that, 1.08 eV, 4.18 eV, 2.28 eV, respectively. For the partially-hydrogen passivated surface, it is assumed to be located the Br-Sty molecule to one of the Si-dimer component, but the other Si-dimer was occupied by one hydrogen. Within this consideration, we have studied Model I and Model II. We have found that adsorption energies of Model I and Model II as 4.29 eV and 0.93 eV, respectively. In our calculations, regarding the adsorption energy for clean and partially-passivated Si surface, the situation is reversed from Model I to Model II.
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