The first-principles investigation on the electronic structure and mechanism of LiH + NH3 → LiNH2 + H2 reaction

First-principle density functional theory calculations were used to investigate the electronic structure and mechanism of the LiH + NH3 → LiNH2 + H2 reaction. Along the reaction pathway, intermediate complexes HLi…NH3 and LiNH2…H2 and a transition state can be found. The N-2p electron in the highest occupied molecular orbital (HOMO) of NH3 transfers to the Li-2s orbital in lowest unoccupied molecular orbital (LUMO) of LiH and forms the initial state HLi…NH3. In the transition state, H1 of LiH and H2 of NH3 turn toward each other, resulting in the formation of a H2 bond. From the transition state to the final state, the geometric configuration changes from Cs to C2v, and the improvement of geometric configuration symmetry results in a decrease in the energy gap between HOMO and LUMO. The LiH + NH3 → LiNH2 + H2 reaction is exothermic.