Enhanced nonlinear optical response of alkaline earthides based on transition metals as a source of excess electrons in the presence of horizontally oriented external electric field
摘要
Geometric, electronic, and nonlinear optical features of a new class of excess electrons, i.e., alkaline earthides have been examined. The rational design principle involves inserting transition metals inside the 36adz to serve as a source of excess electron for Mg metal doped on the outer face of the cage, i.e., M+(36adz)Mg− (where M+ is V to Zn). By using 36adz as a complexant, eight different complexes are investigated. The electronic and thermodynamic stability of complexes is evaluated from their vertical ionization potential and interaction energies, respectively. The true alkaline earthide feature of the complexes is validated through natural bond orbital (NBO) charges, molecular electrostatic potential (MEP), and frontier molecular orbital (FMO) analysis. Further validity of the earthide feature of computed complexes is signified graphically through spectra of partial density of states (PDOS). Moreover, the HOMO–LUMO energy gap (H–L gaps) of all compounds are very small (2.40 to 5.51 eV), when compared with the H–L gap of pure cage, i.e., 8.50 eV. All these properties reward the complexes with quite small values of transition energies ranging from 0.79 to 1.19 eV which ultimately results in unusually enhanced hyperpolarizability up to 6.17 × 105 au for Zn+(36adz)Mg− compound of the series. Furthermore, the hyperpolarizability projection over dipole moment is determined by calculating βvec values. Additionally, the application of an external electric field (EEF) on the computed complexes increases the hyperpolarizability further. The notable enhancement of 1000-fold in hyperpolarizability has been seen for Cr+(36adz)Mg− compound after applying EEF, i.e., from 2.26 × 104 au to 1.5 × 107 au, when compounds are exposed to EEF of 1 × 10−3 au strength.