The Non-linear Optical Properties And The Electric Effect Of Some Electrides And Molecules

The nonlinear optics plays an important role inmanyfields, such asoptical process of information, optical computer,optical communication,etc. The research of the nonlinear optical materials isone of theinternational frontier topics at the present. The searching and designing ofhigh-performance NLO materials is very important in this field.Someprevious investigations find that the electrides with excess electron areexcellent NLO materials with considerable NLO response. The externalelectric field can affect the structure and properties of molecules and theunordinary electric field effect occurs. In this thesis, thenonlinear opticalproperties of the electride molecules and the electric field effect for thestructures andnonlinear optical properties of some important smallmolecules are investigated by the quantumchemical methods-ab initioand density functional theory （DFT）. The maincontributions are asfollowings:1. The structures and properties of the multi Li-doped chainmolecules H（HC=N-Li）nH （n=1-6） are researched. Interestingly,with the increasing of chain length n, two kinds of moleculesemerge. For n=1,2, the Li-salt molecules are formed because the excess electron orbitals are unoccupied. But for n=3-6, excesselectron orbitals are occupied and multi-Li electrides withwide-range excess electron cloud are formed. For the multiLi-doped chain system, the dependence on NLO properties isunordinary stepped increase,2179and2776（n=1and2）<5492and5487（n=3and4）<15235and15377au （n=5and6）. It isshown that multi-Li doping can generates wide-range excesselectron cloud and large NLO response. The new knowledgeenriches the design ideas for NLO materials.2. A new kind of electride molecular salts e^-@C₂₀F₁₉-（CH₂）₄-NH₂M⁺/M₃O⁺（M=Li, Na, and K） has been designed.We usethe C₂₀F₁₉cageas the strong acceptor,the NH₂M/M₃O （M=Li, Na, and K） as donorsand （CH₂）₄chain as unusual bridge.The new electride molecular salts haveexcess electron, which is favor for enhancing NLO response.The excesselectron is pushed out from the （super）alkali atomM/M₃O by the lone pairof NH₂in the donor and further pulled to inside the hole cage C₂₀F₁₉acceptor through the efficient long σ chain （CH₂）₄bridge.It brings largeNLO response for the new designed electride molecular salts.For thee^-@C+20F₁₉-（CH₂）₄-NH₂Na, its large first hyperpolarizability （β0）reaches up to9.5×106a.u. which is about2.4×104times of400a.u. for therelative e-@C₂₀F20Na+without the extended chain （CH₂）₄-NH₂. It isshown that the new strategy is considerably efficient in enhancing the NLO response for the salts.And the effects of different bridges and alkaliatomic number on β0are also exhibited.3. How to generate a non-zero first hyperpolarizability forcentrosymmetric molecule is a challenging question. We use anexternal （pump） electric field to break the centrosymmetry ofelectron cloud and make the centrosymmetric benzene moleculegenerate a non-zero value of the electric field induced firsthyperpolarizability （βF）. Two interesting rules are exhibited.1.TheβFis anisotropic for different directional fields （Fi, i=X, Y, Z）.2.The field dependence of βFis non-monotonic function, and anoptimum external electric field causes the maximum value of βF.The largest first hyperpolarizability βFreaches up to considerable3.9×105a.u. under FY=330×10-4a.u. for benzene. The externalelectric field also can affectthe NLO properties ofnon-centrosymmetric edge-modified graphene ribbonH₂N-（3,3）ZGNR-NO2. The first hyperpolarizability is2.1×107a.u.under FX=600×10-4a.u. for H₂N-（3,3）ZGNR-NO2.It is shown thatthe external electric field can not only create a non-zero firsthyperpolarizability for centrosymmetric molecule, but alsoremarkably enhance the first hyperpolarizability fornon-centrosymmetric molecule.4. Polywater, as a well-known example of pathological sciencedue to as a hypothetically polymerized form of water, hasbeen spread in scientists and the public over40years. Nowadays,this traditional conceptshould still be kept? Noteworthily, anunexpected discovery with unusualsignificance has occurred thatunder high electric field （≈1V/） water moleculesarepolymerizedforming novel water whiskers on the field emitter tipsurface. Theoreticalresearches support the formation of waterwhiskers. Of course，someone will think that would water whisker isreal polywater? A key issues need to be addressed is to find out theunordinary nature of intermolecular interaction in the interestingwater whiskers. Based on our research including evolutions ofstructure, intermolecular interaction and molecular orbitals, truly,wediscover theoretically that unordinary strong H-bond withunordinarycovalent characteristics exists in the water whiskers withvery short H-bond lengths. For example, in the water dimer whisker,its H-bond has the bond length of-25%, covalent bond order（Wiberg bond index） of9times and H-bond energy of5timescompared to the normal H-bond in （H₂O）2cluster. Thus, the newstrong H-bond with unordinarycovalent characteristics is named asthe covalentH-bond. As the covalentH-bond found inwater whiskeris enoughstrong （as new molecular interaction）, leading to anextraordinary polymer effect, andfancifully and really polymerized formof water, the linearwater whisker isjust realone-dimensional polywater. Obviously, it is very different from thewater cluster with usual weak H-bond. And an instance oftwo-dimensional polywater is also found theoretically. Certainly, itis indicated that polywater is subsistent, at least forone-dimensional polywater. Therefore, the traditional conceptshould be^-reconsidered thatpolywateris hypothetical andan exampleof pathological science.