A theoretical study of the structures and chemical bonds of neptunium (III) molecules by a density functional method

In this paper, equilibrium structures and chemical bond characteristics of neptunium trihalide molecules NpX 3 (X = F, Cl, Br and I) have been investigated by using density functional theory (DFT). The influences of the size of the relativistic effective core potential (RECP) have been examined on the molecular structures. The chemical bond characteristics have also been systematically studied by calculating the density of states (DOS), bond length differences and electronic charge distributions. We have determined that the chemical bonds are mainly ionic in those molecules, and the covalency is enhancing while ionicity decreases from NpF 3 to NpI 3 . The calculated bond energies show that the interaction strength in NpX 3 molecules becomes weaker as the halogen atoms becoming heavier.