The important role of superalkalis on the static first hyperpolarizabilities of new electrides: Theoretical investigation on superalkali-doped hexamethylenetetramine (HMT)

Abstract On the basis of Hexamethylenetetramine (HMT), a new class of (super)alkali-doped electrides HMT−X, HMT−FX 2 , and HMT−OX 3 (X = Li, Na, and K) were designed in theory. The results reveal that superalkali FX 2 and OX 3 can keep their structural integrity in these studied compounds. These electrides possess significantly large first hyperpolarizabilities ( β 0 ) in the range of 0.65 × 10 3 –4.72 × 10 5 au due to diffuse excess electrons from chemical doping. It is found that the superalkali effect on the β 0 value is more significant than that of simple alkali doping. Furthermore, employing the heavier superalkali (FK 2 and OK 3 ) can dramatically enhance the β 0 values of the HMT−FK 2 and HMT−OK 3 . The further investigations show that small transition energies is the decisive factor for the large β 0 values of (super)alkali-doped electrides. The ratios between the vibrational and electronic contributions on (hyper)polarizability demonstrate that the vibrational contributions play an important role in determining the static (hyper)polarizabilities. This paper not only designs novel electrides with large NLO response but also expands the application range of superalkali cluster.