Theoretical Studies On Nonlinear Optical Properties Of Some (Super) Alkali-doped Compounds

In the rapidly developing information age,nonlinear optical materials have a wide application prospect in the optical calculation,optical communication and optical information storage.The designing and development of new high-performance NLO materials are always the research direction of many scientists.Some?super?alkali-doped NLO systems have been theoretically studied using ab initio quantum chemistry method.The geometric structures,electronic properties and nonlinear optical properties of these systems have been studied in detail.The main contributions are as follows:1.On the basis of ab initio method,the alkali-doped electrides B₁₂N₁₂-M?M=Li,Na,K?were designed and systematically studied.Doping of alkali metal atom can significantly narrow the wide HOMO–LUMO gap of the B₁₂N₁₂.The NBO analysis and diffuse HOMO orbitals reveal that the doped alkali atoms could be polarized to form diffuse excess electron,leading to a decrease in the transition energies??E?.Thus,these alkali-doped compounds possess significantly large first hyperpolarizabilities??₀=1537—18889 au?,much larger than that undoped B₁₂N₁₂.Consequently,the alkali-doped B₁₂N₁₂ compound may be a potential promising NLO nanomaterial.2.Based on stable all-cis 1,2,3,4,5,6-hexafluorocyclohexane?F₆C₆H₆?,a series of alkali-doped electrides M-F₆C₆H₆?M=Li,Na,and K?were theoretically constructed.The results show that doping of alkali metal atoms narrowed the HOMO–LUMO gap of the F₆C₆H₆.Moreover,the?₀ of these electrides can be sharply increased due to the formation of the diffuse excess electrons.Among these electrides,the largest?₀ of the Li-F₆C₆H₆ is7.00×10⁵ au,which is about 3030 times larger than pure F₆C₆H₆.The larger?₀ values are attributed to the lower?E of these systems.Further,Li-doped dimer and trimer of F₆C₆H₆exhibited unusual electride's features and exhibit dramatically large?₀.Thus,alkali-doped F₆C₆H₆ compounds may be potential candidates for high-performance NLO materials.3.On the basis of Hexamethylenetetramine?HMT?,a new class of?super?alkali-doped electrides HMT-X,HMT-FX₂,and HMT-OX₃?X=Li,Na,and K?were designed theoretically.The integrity of FX₂ and OX₃ units is well maintained in the corresponding compounds.These electrides exhibit considerable large first hyperpolarizabilities??₀?due to diffuse excess electrons from?super?alkali metal doping.It is found that the superalkali effect on the?₀ value is more significant than that of simple alkali doping.In particular,employing the heavier superalkali?FK₂ and OK₃?can more effectively enhance the?₀ of the HMT.According to the two-level expression,small values of?E is an important factor for the large?₀ values of?super?alkali-doped electrides.Thus,superalkali cluster can be used as building blocks to design NLO molecules with large ?₀ values.