Competition between Alkalide Characteristics and Nonlinear Optical Properties in OLi3-M-Li3O (M=Li, Na and K) Complexes

Alkalides possess enhanced nonlinear optical (NLO) responses due to localization of excess electrons on alkali metals. We have proposed a new class of alkalides by sandwiching alkali atoms (M) between two Li3O superalkali clusters at MP2/6-311++G(d,p) level. We notice a competition between alkalide characteristics and NLO properties in OLi3-M-Li3O (M=Li, Na and K) isomers. For instance, the atomic charge on M (qM) in D2h structure is -0.58e for M=Li and its first static mean hyperpolarizablity (\b{eta}o) is 1 a.u., but in C2v structure, qM=-0.12e and \b{eta}o= 3.4*103 a.u. More interestingly, the \b{eta}o value for M=K (C2v) increases to 1.9*104 a.u. in which qM=0.24e. These findings may provide new insights into the design of alkalides, an unusual class of salts and consequently, lead to further researches in this direction.