Theoretical study on superalkali (Li-3) in ammonia: novel alkalides with considerably large first hyperpolarizabilities

Superalkali Li-3 dissolved in gaseous ammonia is investigated by density functional theory. Similar to the lithium atom, Li-3 can coordinate up to four ammonia molecules. Among the structural isomers of Li-3(NH3)(n) (n = 1-4), the one with separately distributed NH3 ligands is preferred. Most of the Li-3(NH3)(n) species possess the alkalide characteristics and exhibit considerably large static first hyperpolarizabilities (beta(0)) up to 3.9 x 10(5) au. Especially, for the lowest-energy Li-3(NH3)(n) complexes, a prominent coordination number dependence of beta(0) is found as follows: 12 608 (n = 1) < 38 564 (n = 2) < 121726 (n = 3) < 391149 au (n = 4). In addition, the case of introducing a Na atom into such superalkali-ammonia systems has been considered and the resulting Li-3(NH3)(n)Na (n = 1-4) complexes are studied in the same vein. It is revealed that the beta(0) values of Li-3(NH3)(n)Na 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.