Extremely large static and dynamic nonlinear optical response of small superalkali clusters NM3M’ (M, M’=Li, Na, K)

Exploring novel nonlinear optical (NLO) materials with excess electron properties is essential for advancing the use of excess electron compounds in optics. The studied superalkali clusters NM3M’ (M, M′ = Li, Na, K) are thermodynamically stable and their binding energies range from −27.10 to −53.84 kcal mol−1. The observed significant values for VIPs suggest their electronic stabilities. Being excess electron candidate these clusters show significant βo value (3.9 × 107 au), which nicely correlates the hyperpolarizability reported by a two-level model (βtl). Furthermore, these clusters exhibit a remarkable static second hyperpolarizability (γo) value of 1.1 × 1010 au for the NK4 superalkali cluster. The hyper Rayleigh scattering (βHRS) is also computed where the highest value of 2.9 × 107 is recorded for NNa3K superalkali. The obtained values of βvec values (projection of hyperpolarizability on dipole moment vector) also signify the excellent nonlinearity of clusters. Besides, the calculated electro-optica pockel's effect β(-ω; ω,0) and second harmonic generation β(-2ω; ω, ω) values are much pronounced at larger dispersion frequency ω = 1064 nm. Moreover, the frequency-dependent second hyperpolarizability γ(ω) with dc-Kerr effect γ(-ω; ω,0,0) and electric field induced second harmonic generation γ(-2ω; ω,ω,0) show larger values at ω = 1064 nm. Thus the highest value of the dc-Kerr constant increases up to 1.0 × 1011 au which also signifies the larger nonlinear refractive index of the studied cluster. We hope this work could open up new possibilities using superalkali clusters as NLO materials for optoelectronics, laser, second harmonic generation and as frequency doubler.