On the potential application of superalkali clusters in designing novel alkalides with large nonlinear optical properties.

A new series of superalkali-based alkalides, i.e., Li3(+)(calix[4]pyrrole)M(-), Li3O(+)(calix[4]pyrrole)M(-), and M3O(+)(calix[4]pyrrole)K(-) (M = Li, Na, and K), have been theoretically designed and investigated by means of density functional theory computations. These species have diverse structural isomers, in which the embedded superalkali units maintain their identities and prefer the horizontal orientation over the vertical one. All the proposed alkalides exhibit considerable first hyperpolarizabilities (β0) up to 34,718 au. Especially, a prominent M(-) atomic number dependence of (hyper)polarizabilities is observed for the Li3(+)(calix[4]pyrrole)M(-) and Li3O(+)(calix[4]pyrrole)M(-) compounds. Besides, the dependence of the nonlinear optical response of such alkalides on the species of involved superalkalis is also investigated. We hope that this work will promote further application of superalkalis and, on the other hand, attract more research interest and efforts in exploring new, unconventional alkalides.