For the O-terminated Cu 2 O(100) and Cu 2 O(111) surfaces, the difference between the DOS for spin-up and spin-down electrons was reported previously. In addition, half-metallic behaviour has been observed for certain Cu 2 O surfaces, and for bulk Cu 2 O with cation vacancies. To gain further insight into the origin of the observed surface magnetism, we additionally performed a Bader charge analysis on all investigated systems. The respective Bader net atomic charges for the Cu and O terminated Cu 2 O(100) surfaces are illustrated in Figure .