| Ammonia borane(NH3BH3), for it’s ultra-high hydrogen storage capacity and lower hydrogen desorption temperature, has been widespread concern around the world. As it can be applied in real life, ammonia borane was modified and metal amidoboranes(eg LiNH2BH3), bi-metal amidoboranes(eg NaLi(NH2BH3)2) and metal amidoborane derivatives(eg LiN2H3BH3) have been synthesized successfully. In this paper, the geometric construction, electronic structure, chemical bonding properties, and thermodynamic properties of LiAB, NaLiAB and LiHB, which represent metal amidoboranes, bi-metal amidoboranes, and metal amidoborane derivatives, respectively, have been comparative studied by based on the primary principle of density functional theory(DFT) calculation. The main contents were as follows:(1) The structure showed that, NaLiAB was orthogonal crystal, which was different from the triclinic crystal of LiAB and Li HB, meanwhile, the small difference of lattice parameter with the experimental values and the optimized values indicated that the construction of the model is reasonable. On this basis, the energy band structure, total density of states and partial density of states described the structural properties of LiAB, Na Li AB and LiHB, the results show that: the band gap of LiAB, Na LiAB and LiHB are wide band gap, as 4.094, 4.067 and 4.434 eV, respectively, and all of them were indirect band gap; the density of states and partial density of states of LiAB, NaLiAB and LiHB described electronic states near the Fermi level, and the bonding situation between B, H atoms and N, H atoms.(2) On the nature of the chemical bond, the Hδ-(B)...Hδ +(N) bond lengths of LiAB, Na Li AB and LiHB were calculated and analyzed and the results are as followed: LiHB was not as stable as LiAB and NaLiAB, and Hδ-(B)...Hδ +(N) of LiHB can react more easily. The analyzed bond angles of LiAB, NaLi AB and LiHB suggest that ∠H-B-H bond angle of LiHB was the largest in them and B atoms had small force binding to H atoms. Then, the charge density and charge density difference of LiAB, Na LiAB and LiHB reflected the nature and intensity of the bond intuitively. The results suggest that the metal atoms(Li and Na atoms) and N atoms were stonger polar ionic bond, while the B, N, and H atoms were less polar covalent bonds with low charge density of states. Next, the bond strength were studied by Mulliken atomic charge and bond population quantifiably. The atomic orbits were described by Mulliken atomic charge and the dihydrogen bond existed. The bond population and the population ionization degree showed that: B-H was covalent bond, Li-N was ionic bond, while N-H were covalent ionic bond. Meanwhile, the Li and N atoms, B and H in LiAB combined closelier than those in NaLiAB and LiHB, while B and N in LiAB more weaklier. Finnally, the caculated hydrogen dissociation energy of LiAB, NaLiAB and LiHB suggested that the B-H in LiHB break more easlier than that in LiAB and NaLiAB, while the N-H in LiAB break more difficultily than that in NaLiAB and LiHB. In addition, the B-H break prior to the N-H in all of them.(3) Based on the theoretical basis of the density functional perturbation theory calculation method, the phonon density of states and thermodynamic properties of LiAB, NaLi AB and Li HB have been obtained. The Phonon results of LiAB, NaLiAB and LiHB indicated that their respective lattice vibration frequencies were between 152-196, 143-189 and 163-205 cm-1; and stretched, rotation, shear cut frequency vibrational modes between each other atoms were within the range of 190-3700 cm-1. Then, on the basis of phonons, the relationship between of the Enthalpy, Entropy, Gibbs free energy and temperature(T) of LiAB, Na Li AB and LiHB have been researched and described with the functions, and the results show that the Enthalpy, Entropy, Gibbs free energy of NaLi AB changed with temperature less than LiAB and LiHB.(4) The hydrogen evolution reaction mechanism of LiAB, Na LiAB and LiHB were researched by the frontier orbital theory and transition state theory, and the results showed that: the HOMO orbital of LiAB and Li HB were contributed by N and H(B) atoms electron wave function, the LUMO orbit were contributed by the N, B and H(N) atoms electron wave function, and hydrogen evolution was mainly through intramolecular reaction; while, the HOMO orbital of NaLiAB were contributed by the same group, and the LUMO orbital of that were contributed by the two groups, which indicated hydrogen evolution reacted in Intermolecular and intramolecular. The energy gap difference values of LiAB, Na LiAB and LiHB were 5.077,4.705 and 4.685 eV, respectively, and the chemical reactivity of them were: LiAB <NaLiAB <LiHB. The barrier of direct reaction of LiAB, NaLiAB and LiHB were 57.12, 56.83 和 54.33 kcal/mol, respectively; while the barrier of indirect reaction of them were 35.21, 34.75, 28.69 kcal/mol.
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