Abstract
Excess electron compounds have been proposed to be novel candidates of high-performance nonlinear optical (NLO) materials because of their large static first hyperpolarizabilities (beta(0)). To enhance the stability of an unstable excess electron compound (LiCN center dot center dot center dot Li) with an extremely large beta(0) value (310196 a.u.), we designed a boron nitride nanotube (BNNT) as a protective shield molecule to encapsulate it (in theory). The stability of LiCN center dot center dot center dot Li was enhanced: the vertical ionization potentials (VIP) of LiCN center dot center dot center dot Li increased after encapsulating. Therefore, by comparison with LiCN center dot center dot center dot Li, the encapsulated complexes are more difficult to oxidize. Significantly, the BNNT encapsulated LiCN center dot center dot center dot Li complex exhibits a considerable beta(0) value (10645 a.u.), which is significantly (almost 380 times) larger than 28 a.u. of BNNT. Our further investigations into the intrinsic hyperpolarizabilites (beta(int)) of these compounds show that there are clearly dependencies of the NLO response on the transition energy. Furthermore, it is easy to encapsulate LiCN center dot center dot center dot Li from the B-rich edge rather than N-rich edge of BNNT due to the lower energy barrier, which makes our calculations more useful to experimentalists who may try to synthesize these compounds. Knowledge of the encapsulation process of LiCN center dot center dot center dot Li within BNNT provides a new strategy for the design and synthesis of stable high-performance NLO materials.