Extremely large nonlinear optical response and excellent electronic stability of true alkaline earthides based on hexaammine complexant

Geometric, electronic and nonlinear optical properties of a new class of excess electron compounds (alkaline earthides) have been investigated. The rational design principle involves judiciously placing alkali metals inside the hexaammine complexant to serve as excess electron source for alkaline earth metals placed outside the complexant By utilizing hexaammine as the complexant, nine different compounds M+ (Hexaammine)M- (M = Li, Na and K: M- = Be, Mg and Ca) are studied. The alkaline earthides are quite stable electronically and thermodynamically, as revealed from their vertical ionization and interaction energies, respectively. The true alkaline earthide characteristic is confirmed through NBO charges and frontier molecular orbital analysis. The alkaline earthides show remarkable nonlinear optical responses with the first hyperpolarizabilities (beta(o)) up to 6.4 x 10(5) au. The higher hyperpolarizabilities values are attributed to the presence of excess electron on alkaline earth metals in polarized p-orbitals which is confirmed through the partial density of states (PDOS) spectral analysis. The hyperpolarizabilities are rationalized through two level method analysis. The projection of hyperpolarizability on the dipole moment is analyzed through beta(vec) calculations. Quite contrary to other excess electron materials, the alkaline earthides show excellent nonlinear optical response despite moderate to high crucial excitation energies. These alkaline earthides will pave the path for further exploration of electronically stable high performance NLO materials. (C) 2019 Elsevier B.V. All rights reserved.