Nonlinear optical properties of KnCl (n = 2–7) superalkali clusters

The lowest energy structures along with the low lying isomer, stabilities, electronic properties, optical properties and nonlinear optical responses of K n Cl (n = 2–7) clusters were studied within the density functional theory. The second order energy difference, dissociation energy and GH-L (HOMO–LUMO gap) point out that K n Cl (n = 3, 5, 7) clusters are more stable. The calculated adiabatic ionization energies (AIE) for the K n Cl (n = 2–6) clusters are in agreement with the measured ionization energies. The optical properties, namely optical electronegativity and refractive index, depends on the GH-L energy values. The K atom capped planar rhombus geometry of the K 4 Cl causes the noticeable vibrational frequency shift compared to the rest of IR spectra of the clusters. The first static hyperpolarizability ( β o ) values are in the range of 2.33 × 10 3 –2.87 × 10 4 au and the second static hyperpolarizability varies between 5.74 × 10 6 au and 38.9 × 10 6 au for the cluster. The nonlinear optical response is due to the superalkali nature of K n Cl (n = 2–7) clusters. From computed β vec values, the hyperpolarizability has projection on the dipole moment vector for the superalkalis except the K 2 Cl and K 5 Cl. The absorption spectra point out that K n Cl (n = 6–7) clusters can be suitable as a NLO material since they have transparency in the deep UV region ( λ < 300 nm).