Nonlinear optical behavior of Li n F (n = 2-5) superalkali clusters.

Hyperlithiated clusters are known for their unusual bonding characteristics and lower ionization potentials. This study reports nonlinear optical (NLO) properties of a series of hyperlithiated clusters, Li n F (n = 2-5) for the first time. The structures of small Li n F (n = 2-5) clusters, obtained using second order Møller-Plesset perturbative method, are found to be stable against eliminations of F, F‾, and LiF. These Li n F species are stabilized by both ionic as well as covalent interactions. Our study shows that Li n F species can be thought of as superalkali-halogen (Li n  - F) clusters but belong to the class of superalkalies themselves. These clusters may also possess alkalide and/or electride characteristics due to excess electrons. The dipole moment, mean polarizability, and hyperpolarizability suggest their significant NLO responses which are explained using the highest occupied molecular orbital surfaces and TD-DFT analysis. The exceptionally large hyperpolarizability of Li2F (~10(5) a.u.) and its electride characteristics are particularly highlighted. This study may guide the researchers in the design of novel materials with significant NLO responses useful for electro-optical applications. Graphical Abstract Li2F superalkali resemble an electride in which the excess electron is pushed out by Li2 (+) moiety, leading to its high hyperpolarizability of order of 10(5) a.u.