Diffuse electron of alkali metals (Li, Na, K) or diffuse electron pair of alkaline earth metals (Be, Mg, Ca) which predict larger second hyperpolarizability? A comprehensive study of M center dot center dot center dot NH3 model compounds

In the present work, model M center dot center dot center dot NH3 complexes of alkali and alkaline earth metals are considered to calculate second hyperpolarizability using HF, MP2, CCSD and DFT methods. The diffuse electrons of alkali metals are more efficient than diffuse electron pair of alkaline earth metals in enhancing the magnitude of second hyperpolarizability. The radiation frequency has a dramatic effect on gamma(av). Although MP2 gamma(zzzz) is overestimated by a smaller margin the corresponding gamma(av) fairly agrees with the CCSD result. The large second hyperpolarizability of alkali metal (versus alkaline earth metal) complexes arises from the lower energy intense transition. (C) 2017 Elsevier B.V. All rights reserved.