Elucidating hydrogen assisting vacancy formation in metals: Mo and Nb as examples An-Yuan Gao, Yue-Lin Liu, Zhen-Hong Dai and Chen Duan Eur. Phys. J. B, 86 8 (2013) 355 Published online: 07 August 2013 DOI: 10.1140/epjb/e2013-40552-x