Calculations of Molecular Structures and Processes Important for Hydrogen Behaviour in the Li-Amide/Imide System

Lithium amide (LiNH2) and imide (Li2NH) have recently attracted much attention as part of the Li-H-N system suitable for hydrogen (H) storage applications. However, the ground-state imide structure is still unknown with at least six candidate structures, with ground state energies all very close to one another. In order to discover possible pathways for the imide-amide-imide transformations during the hydrogen absorption/desorption cycles, we have examined the molecular structures involved (along with their changes during these processes) using ab-initio calculations based on the linear combination of atomic orbitals (LCAO). In addition, the influence of Li substitution by some other elements of interest on the system behaviour was investigated. These analyses were complemented by density functional theory (DFT) calculations of several crystal structures appearing in the processes. In this way a thorough insight into the structures and the processes taking place at atomic level is attained, providing a starting point for understanding these complicated systems, and the mechanisms governing their transformations.