Theoretical study on superalkali (Li3) in ammonia: novel alkalides with considerably large first hyperpolarizabilities

Abstract

Superalkali Li₃ dissolved in gaseous ammonia is investigated by density functional theory. Similar to the lithium atom, Li₃ can coordinate up to four ammonia molecules. Among the structural isomers of Li₃(NH₃)_n (n = 1–4), the one with separately distributed NH₃ ligands is preferred. Most of the Li₃(NH₃)_n species possess the alkalide characteristics and exhibit considerably large static first hyperpolarizabilities (β₀) up to 3.9 × 10⁵ au. Especially, for the lowest-energy Li₃(NH₃)_n complexes, a prominent coordination number dependence of β₀ is found as follows: 12 608 (n = 1) < 38 564 (n = 2) < 121 726 (n = 3) < 391 149 au (n = 4). In addition, the case of introducing a Na atom into such superalkali–ammonia systems has been considered and the resulting Li₃(NH₃)_nNa (n = 1–4) complexes are studied in the same vein. It is revealed that the β₀ values of Li₃(NH₃)_nNa are influenced by both the coordination number and the relative position of NH₃ ligands. We hope that this study could provide a new type of alkalides and raise the possibility of exploring a fresh, thriving area, i.e. superalkali solutions with solvents of all sorts.