The Hartree-Fock-Slater (HFS) calculations of a CH 3OCu 5 cluster symbolizing methoxide bound to a Cu(100) surface are presented. Adsorption geometry, molecular orbitals, and symmetry properties of the CH 3O group in terms of one-electron energies, charge distributions, and partial densities of states (PDOS) are discussed. A comparison of calculated ionization energies and measured binding energies supports the occupation by methoxide of the hollow adsorption site. The electron distribution of the hydrogen atoms has been analyzed for different geometries and is shown to be a sensitive probe of the oxidation from methoxide (CH 3O)/methyl (CH 3) to formaldehyde (CH 2O)/methylene (CH 2).