Crystal and electronic structures of solid M(NH₂BH₃)_n (M = Li, Na, K) and the decomposition mechanisms

Metal amidoboranes (MABs) are the important candidates for on board hydrogen storage materials with some excellent properties. In this paper, the traditional crystal structures of LiNH₂BH₃, NaNH₂BH₃ and KNH₂BH₃ (LAB, SAB and KAB for short, respectively) have been studied by using first-principle density functional theory. First of all, the periodic structures of LAB and SAB have been predicted by Monte-Carlo simulation. Then all of the MABs have been optimized by the DFT method. The electronic structures and phononic density of states indicate the sequences of the stability and the hydrogen properties. The dehydrogenation process has been designed for the three MABs as nMNH₂BH₃ → nMNBH + 2nH₂ based on the experiment. The sequence of the decomposition rates of the dehydrogenation should be as LAB > KAB > SAB.