The main factors influencing the O vacancy formation on the Ir doped ceria surface: A DFT+U study Z. X. Yang, D. W. Ma, X. H. Yu and K. Hermansson Eur. Phys. J. B, 77 3 (2010) 373-380 Published online: 01 October 2010 DOI: 10.1140/epjb/e2010-00295-x