Ab initiocalculations of selected ionization states of Cu on MgO(001)

Abstract

The oxidation states of Cu on the MgO(001) surface are studied using an ab initio cluster (five atoms plus charge array) calculation in the Hartree-Fock approximation, for two cases: (i) Cu above a surface oxygen and (ii) Cu in a surface Mg vacancy. Cu binds slightly atop oxygen with a binding energy comparable to room temperature. Above a Mg vacancy it binds strongly with binding energy of about 9 eV, and it stays stably at about 1 bohr above the surface as a ${\mathrm{Cu}}^{2+}$ ion: A Cu atom donates two electrons to empty antibonding surface orbitals of the surrounding surface oxygens. A ${\mathrm{Cu}}^{+}$ ion donates one electron to a similar surface orbital. A ${\mathrm{Cu}}^{3+}$ ion cannot stay stably in a Mg vacancy.