Germanium-based superatom clusters as excess electron compounds with significant static and dynamic NLO response; a DFT study.

Herein, the geometric, electronic, and nonlinear optical properties of excess electron zintl clusters Ge 5 AM 3 , Ge 9 AM 5 , and Ge 10 AM 3 (AM = Li, Na, and K) are investigated. The clusters under consideration demonstrate considerable electronic stability as well as superalkali characteristics. The NBO charge is transferred from the alkali metal to the Ge-atoms. The FMO analysis shows fabulous conductive properties with a significant reduction in SOMO-LUMO gaps (0.79-4.04 eV) as compared with undoped systems. The designed clusters are completely transparent in the deep UV-region and show absorption in the visible and near-IR region. Being excess electron compounds these clusters exhibit remarkable hyperpolarizability response up to 8.99 × 10 -26 esu, where a static second hyperpolarizability ( γ o ) value of up to 2.15 × 10 -30 esu was recorded for Ge 9 Na 5 superatom clusters. The excitation energy is the main controlling factor for hyperpolarizability as revealed from the two-level model study. The electro-optical Pockel's effect and the second harmonic generation phenomenon (SHG) are used to investigate dynamic nonlinear optical features. At a lower applied frequency (=532 nm), the dynamic hyperpolarizability and second hyperpolarizability values are significantly higher for the studied clusters. Furthermore, for the Ge 9 K 5 cluster, the hyper Rayleigh scattering (HRS) increases to 5.03 × 10 -26 esu.