1. How can the surface magnetism of Cu 2 O surfaces with an excess of oxygen be explained? According to the Bader charge analysis, fewer electrons are localized at the outermost O and Cu atoms of the Oexcess Cu 2 O surfaces than at the respective atoms in the bulk. This implies that the 3d and 2p electron orbitals of these outermost Cu and O atoms are not completely occupied. We, therefore, assume that unpaired 2p and 3d electrons of the outermost O or Cu atoms lead to the observed local magnetic moments and, thus, to the surface magnetism.