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运用基于密度泛函理论框架下的第一性原理方法,研究了储氢材料LiNH_2BH_3的高温相(α-LiHB),低温相(β-LiHB)和LiNH_2BH_3(LiAB)的晶体结构,能带结构,态密度以及化学键性质。氢原子解离能的计算表明与Li~+相邻的H~(δ+)(N1)在初始析氢阶段起主导作用,低温β-LiHB较高温α-LiHB更易于析氢。然后,通过Dmol3计算的HOMO和LUMO图表明α-LiHB可能析氢途径为H-N_1…B和H-N_2…B,而β-LiHB和LiAB仅有H-N_1…B途径。HOMO-LUMO的能隙大小表明LiAB,α-LiHB和β-LiHBH的化学稳定性为:LiAB>α-LiHB>β-LiHB。以上所有研究都为实验合成的多相LiHB提供了一定的理论基础。
The first-principles method based on density functional theory (DFT) was used to study the crystal structure, energy band structure, thermal stability and thermal stability of LiNH_2BH_3, which are high temperature phase (α-LiHB), low temperature phase (β-LiHB) and LiNH_2BH_3 (LiAB) State density and chemical bond properties. Calculations of the dissociation energies of hydrogen atoms indicate that H ~ (δ +) (N1) adjacent to Li ~ + plays a leading role in the initial hydrogen evolution phase, and the higher temperature α-LiHB of low temperature β-LiHB is easier to hydrogen evolution. Then, the HOMO and LUMO maps calculated by Dmol3 show that the possible hydrogen evolution pathways for α-LiHB are H-N_1 ... B and H-N_2 ... B, whereas β-LiHB and LiAB have only the H-N_1 ... B pathway. The energy gap size of HOMO-LUMO indicates that the chemical stability of LiAB, α-LiHB and β-LiHBH is LiAB> α-LiHB> β-LiHB. All the above studies provide some theoretical basis for the experimental synthesis of multi-phase LiHB.