Our first-principles study of Ca(NH2BH3)(2) reveals that the gas phase energy barrier for the first H-2 release is 1.90 eV via a Ca center dot center dot center dot H transition state and 1.71 eV via an NIH center dot center dot center dot B transition state for the second H-2 release. In the dimer, the barrier for H-2 release from the bridging [NH2BH3](-) species is 1.60 eV via an N-H center dot center dot center dot B transition state, and 0.94 eV via an N-H center dot center dot center dot B transition state for the non-bridging [NH2BH3](-) species. Analysis of the atomic charge distribution shows that the mechanism of dehydrogenation is determined by the charge transfer between the transition state and the initial state: the less the charge transfer, the lower the barrier to dehydrogenation. Copyright (C) 2013, The Authors. Published by Elsevier Ltd. All rights reserved.