Adsorption of Methanol and Methoxy on Cu（111） Surface： A First-principles Periodic Density Functional Theory Study

Adsorption of methanol and methoxy at four selected sites （top, bridge, hcp, fcc） on Cu（111） surface has been investigated by density functional theory method at the generalized gradient approximation （GGA） level. The calculation on adsorption energies, geometry and electronic structures, Mulliken charges, and vibrational frequencies of CH3OH and CH3O on clean Cu（111） surface was performed with full-geometry optimization, and compared with the experimental data. The obtained results are in agreement with available experimental data. The most favorite adsorption site for methanol on Cu（111） surface is the top site, where C-O axis is tilted to the surface. Moreover, the preferred adsorption site for methoxy on Cu（111） surface is the fcc site, and it adsorbs in an upright geometry with pseudo-C2v local symmetry. Possible decomposition pathways also have been investigated by transition-state searching methods. Methoxy radical, CH3O, was found to be the decomposition intermediate. Methanol can be adsorbed on the surface with its oxygen atom directly on a Cu atom, and weakly chemisorbed on Cu（111） surface. In contrast to methanol, methoxy is strongly chemisorbed to the surface.