Oxacarbon superalkali C3X3Y3 (X = O, S and Y = Li, Na, K) clusters as excess electron compounds for remarkable static and dynamic NLO response

Abstract

An intriguing class of excess electron oxacarbon superalkali clusters is explored for nonlinear optical response through density functional theory (DFT) methods at CAM-B3LYP/6–311++G(d,p). These superalkali clusters shows noticeable binding energies per atom (Eb) which reveals their thermodynamic stabilities (−86.45 ∼ −119.44 kcal mol−1). The obtained significant VIPs values also suggest the electronic stability of these clusters. The VIP values range from 2.06 eV to 3.42 eV. These clusters show remarkable electronic properties and their HOMO-LUMO gaps (EH-L) are significantly reduced. The lowest H-L gap of 0.96 eV is obtained for C3O3K3 while the highest H-L gap of 2.07 eV is calculated for C3S3Li3. The obtained PDOS spectra further provide evidence for the superior electronic properties of these clusters. The clusters show excellent nonlinear optical properties as revealed from remarkable values (1.6 × 106 au) of static first hyperpolarizability. The controlling factors for hyperpolarizability are also explored by using conventional two-level model. The calculated values of βo are correlated nicely with βtl. The crucial excitation energy is the key factor in controlling the first hyperpolarizability. In these excess electron clusters, the second hyperpolarizability (γo) response increases up to 4.3 × 109 au. Moreover, the calculated scattering hyperpolarizability (βHRS) values are quite significant in these clusters and the highest value of 1.3 × 106 au is calculated for C3S3K3. Additionally, these clusters also possess larger dynamic nonlinearities. The dynamic second hyperpolarizability with dc-Kerr effect increases up to 1.0 × 1011 au. The remarkable values for refractive index (n2) also suggest the excellent nonlinearity of these superalkali clusters.