Theoretical investigation of lithium-based clusters Lin (where n = 3, 5, 7) with remarkable electronic and frequency-dependent NLO properties
Department of Chemistry, COMSATS University Islamabad, Abbottabad Campus, 22060, Abbottabad, KPK, Pakistan
Accepted: 17 June 2022
Published online: 11 July 2022
Herein, we report the theoretical insight into electronic and nonlinear optical (NLO) properties of pure lithium clusters Lin (where n = 3, 5, 7) using MP2/6–311++G(d,p) and DFT theory. The optimization of clusters is carried out at MP2/6–311++G(d,p), while spectral, electronic, and NLO properties are at CAM-B3LYP functional. The studied superalkali clusters are thermodynamically stable, and their binding energies per atom range from − 8.15 to − 15.49 kcal mol−1. The calculated vertical ionization potentials (VIP) and FMOs analysis suggest their superalkali and excess electrons nature. These clusters have significantly reduced HOMO–LUMO gaps (2.78–3.41 eV). The displayed total density of states (TDOS) spectra also provide a more comprehensive picture of electronic characteristics. Being excess electron clusters, the static hyperpolarizability (βo) value is up to 7.77 × 104 au for Li5 where its second hyperpolarizability (γo) significantly increased up to 2.7 × 106 au. There is an excellent correlation between total hyperpolarizability and the computed vector part of hyperpolarizability (βvec). The two-level model (βtl) reveals that excitation energy is the main influencing factor to hyperpolarizability. Besides, dynamic hyperpolarizabilities β(ω) show remarkable values (3.2 × 106 au) for EOPE β( − ω;ω,0) effect at 532 nm. Similarly, the second-harmonic generation (SHG) phenomenon is also much more pronounced at a small dispersion frequency (ω = 532 nm). The dynamic second hyperpolarizability γ(ω) value increases up to 1.2 × 1011 au, and the results are much more pronounced at a larger dispersion frequency (1064 nm). Additionally, the dynamic NLO properties at the applied frequency of 1300 nm are much more pronounced than those of 1900 nm. The significant scattering hyperpolarizability (βHRS) is recorded up to 1.3 × 104 au for Li3 cluster. Hence, the studied lithium-based superalkali clusters are novel candidates for excellent electronic and NLO properties.
© The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2022