Theoretical investigation of superalkali clusters M2OCN and M2NCO (where M=Li, Na, K) as excess electron system with significant static and dynamic nonlinear optical response

Abstract

Confining excess electrons in a specific space is an effective strategy to design high-performance nonlinear optical (NLO) materials. Herein, with the aid of density functional theory (DFT) calculations, we investigated the nonlinear optical (NLO) properties of excess electron superalkali/supermetals M2OCN and M2NCO (where M = Li, Na, K) clusters. The electronic and optoelectronic properties of these superalkali clusters are studied at CAM-B3LYP/6−311+G(d,p) level of theory. The studied clusters possess significant thermal stability and their binding energies per atom are in the range of -120.98 to -128.04 kcal mol−1. Furthermore, the analyzed superalkali clusters show excellent electronic properties. Being excess electron candidate, these supermetals clusters show significant reduced HOMO-LUMO gaps (-4.40 ∼ 2.79 eV). The HOMO-LUMO gaps are further reduced for M2NCO configuration that reveals excellent conductive properties. The further comprehensive piture of electronic properties is obtained from the plotted density of states (DOS) analysis spectra. With the justified excess electron character, the static hyperpolarizability (βo) response increases up to 1.4 × 104 au. The strong resemblance of total hyperplarizability with βvec provides evidence for practical design of NLO materials. Moreover, the hyperpolarizability from the two-level βtl model nicely correlates with βo. Besides, static nonlinearity, frequency-dependent hyperpolarizability (β(ω)) shows remarkable values for electro-optical pockel’s effect β(-ω;ω,0) at dispersion frequency of 532 nm whereas, the second harmonic generation (SGH) phenomena is much pronounced at higher frequency (ω = 1064 nm). The obtained second hyperpolarizability (γ(ω)) response increase up to 2.1 × 108 au. The dc-Kerr effect (nonlinear refractive index) γ(-ω;ω,0,0) shows a remarkable response (2.1 × 1010 au) at ω = 532 nm.