Li_2NH晶体结构建模和电子结构的第一性原理研究

基于密度泛函理论的赝势-平面波方法,采用三种模型分别研究Li,N原子对N—H键方位的影响以及N—H键间的相互影响,得到了Li2NH的晶体结构和H原子的占位位置.计算结果表明:Li2NH晶体为层状结构,空间群为P42,晶胞中4个N—H键分为两层,层内N—H键为反平行排列,层间N—H键为垂直排列.态密度和电子局域函数(ELF)分析表明,N—H键呈明显的共价键特性,Li和N—H键呈明显的离子键相互作用.可逆储氢反应Li2NH+H2/LiNH2+LiH在温度0K时的反应焓为69.6kJ/molH2,与实验结果66kJ/molH2符合得较好.

Ab initio structural simulation and electronic structure of lithium imide

The crystal structure and the locations of the hydrogen of lithium imide(Li_2NH)are studied by first-principle plane wave pseudopotential method based on the density function theory(DFT).Three models are used to investigating the effects of the Li,N and nearest-neighbor N-H bonds to N-H bond orientation,respectively.The calculated results show that Li_2NH crystal can be described by a layered tetragonal crystal(P4_2)structure.Four N-H bonds of each conventional cell align in two layers.The two imide groups in the same layer prefer to be antiparallel and the imide groups in the nearest-neighbor layers tend to be vertical.The density of states(DOS)and the electron local function(ELF) analysis show strong ionic interaction between the Li and N-H dimmer,while the bonding between the N and H has covalent character.Our P4_2 structure of Li_2NH crystal yields a hydrogen storage Li_2 NH_2+H_2/LiNH_2+LiH reaction enthalpy of 69.6 kJ/mol H_2 at T=0 K,in good agreement with experimental reports of 66 kJ/mol H_2 for this reaction.