This Letter reports static and dynamic second hyperpolarizabilities of the lithium salt of pyridazine Li-H3C4N2 and lithium salt electride Li-H3C4N2 center dot center dot center dot Na-2. The results show strong dependence of the computed values with respect to the electron correlation treatment. The static value obtained at the CCSD level with the aug-cc-pVDZ basis set for the Li-H3C4N2 center dot center dot center dot Na-2 is 1.1 x 10(9) au. This extremely large value of the second hyperpolarizability reinforces the potential of this system for application in nonlinear optics. (C) 2015 Elsevier B.V. All rights reserved.