Pressure-induced structural transitions of LiNH2: A first-principle study

Abstract: The pressure-induced phase transformations in LiNH2 have been studied by using ab initio total-energy calculations and evolutionary structure prediction simulations. Two stable high-pressure polymorphs of LiNH2 are found: β-LiNH2 (orthorhombic, NaNH2-type, Fddd) and γ-LiNH2 (orthorhombic, P21212). The β→γ structural transition occurs at 10.7GPa, which is in good agreement with experimental observation. Further analysis of the structural properties, charge density distribution, and calculated phonon density of states indicates that the possibility of the N–H⋯N hydrogen bond occurring in the high-pressure γ-LiNH2 is extremely high. The existence of hydrogen bond weakens the N–H polar covalent bonds within NH2 groups, which can facilitate the hydrogen desorption. [Copyright &y& Elsevier]