Theoretical Studies On Nonlinear Optical Properties From Small Molecule Systems To Nanomolecule

In today's high-tech world, photonic materials have wide application in manyfields, such as optical communication, optical process of information, opticalcomputer, etc. The research of the nonlinear optical (NLO) materials and the NLOproperties is the important field of the optical communication technology. It is alsoone of the present international frontier topics. The searching and designing ofhigh-performance NLO materials are important base in the field. In this paper, thestructures and nonlinear optical properties of some important structures from smallmolecule systems to Nanomolecule are investigated by using the quantum chemicalmethods-ab initio and density functional theory (DFT). The main contributions of thispaper are as following:1．The three structures of rare gas inserted fluorohydrides HRgF(Rg=He, Ar andKr) with all real frequencies are obtained at the QCISD(T)/aug-cc-pVTZ level. Thestatic first hyperpolarizabilities (β0) at the QCISD/aug-cc-pVQZ level are8a.u.(HF),384a.u.(HHeF),737a.u.(HArF), and465a.u.(HKrF). The β0value remarkablyincreases by about50–90times from8a.u.(HF) to384–737a.u.(HRgF) due to theinserted rare gas (Rg). The Rg atomic number dependence of β0for HRgF (Rg=He, Ar,and Kr) is found at the first time. The order of β0is unmonotonic to be HHeF <HArF> HKrF. The Rg atomic number dependence of β0relates to both the geometric effect(expanded H…F distance by Rg) and the electronic effect of Rg. Thus, the rare gasatomic number dependence of β0is unmonotonic.2. A new strategy of the combination effects of both push and pull electrons of thecomplexant to enhance the first hyperpolarizability is performed with two Li atomdoped complexants with a pair of difluorophenyl subunit rings. Large variance of thestatic first hyperpolarizabilities (β0) are exhibited at the MP2/6-311++G(d,p) level.The order of the β0values is2.9×10~2(complexant UD)<<5.9×10~3(LL)<1.9×10~4(H-L)<2.3×10~4(HF-L)<3.2×10~4(L-L)<7.8×10~5a.u.(HF-LF). It is found thatHF-LFwith the edge-type push–pull electronic effect of the complexant has the largestβ0. This work may contribute to the development of potential high-performance nonlinear optical materials.3. This paper exhibits the role of defects on the static first hyperpolarizability (β0)for topological Stone-Wales (SW), single vacancy (SV) and double vacancy (DV)defects. For eight carbon nanotubes with defects and one relevant perfect nanotube,the obtained order of the b0values is0(Perfect)<5.0×10~2(DV585-z)<5.3×10~2(SW5577-z)<4.6×10~3(DV585-xz)<6.0×10~3(DV555777)<7.3×10~3(SV-xz)<1.1×10~4(SV-z)<3.3×10~4(SW5577-xz)<2.2×10~5a.u.(SW57-75). Four interestingrelationships between the defect and the β0value are observed.(1) The defects bring alarge increase of the β0values.(2) For the SW and DV defects, the direction of thedefect is an important factor to enhance the β0value.(3) Interestingly, not vacancydefects but the topological defect can bring the largest β0value.(4) For thetopological SW defects, the separate pentagon-heptagon pair defect may be moreefficient than the fused one to enhance the β0value.