| Nonlinear optical?NLO?materials are widely used in the fields of optical communication,optical computer,optical storage and other high-tech fields,which promote the search and design of high-performance NLO materials.The intensity of nonlinear optical response is mainly measured by nonlinear optical coefficients.Therefore,the main task of study the high performance nonlinear optical materials is to improve the nonlinear optical coefficients of the systems.In this paper,quantum chemical methods were used to study the nonlinear optical properties of some nanostructures.The main contents of this paper are as follows:1.The article studied various type of push-pull electron group end position replacing electronic structure of H??CH?CH?n?H,and calculated the influence of push electron donating group??NH2,?OH,?NHCOH,?CH3?and pull electron donating group??F,?Cl,?C6H5,?C?CH,?CN,?CHO,?NO2?on nonlinear optical properties of long-rang conjugate alkene molecular structure at the level of LC-BLYP/6-31G?d?.The results showed that either pure pushing or pulling the electron group can enlarge the hyperpolarizability?0?a.u.?of conjugate alkene structure.?0 enlarges from 0.6 of H??CH?CH?n?H structure to 4.0×103 of NH2??CH?CH?6?H and 5.4×103 of H??CH?CH?6?NO2 individually.Pulling and pushing electron group connecting both ends of conjugating alkene plays synergistic effect on the existence of?0,the synergistic role of?NH2 and?NO2 is most obvious,apart from the attribution of pure?NH2 and pure?NO2 replacement on?0,the synergistic effect??=4.6×103 a.u..?0 enlarges from0.6 of H??CH?CH?6?H to 1.4×104 a.u.of NH2??CH=CH?6?NO2,increased about2.3×104 times.?0 of structure NH2??CH=CH?6?NO2 enlarges as the length of the extent of chain length.A new stratregy of push-pull electron group synergistic effect to enhance the molecular structure nonlinear optical property was raised.2.Interesting effects of doped boron?B?atoms on the static first hyperpolarizabilities??0?for boron edge-doped single-walled carbon nanotubes?SWCNTs?are revealed.The results show that the boron edge-doped bring a large increase of the?0 values.The obtained order of the?0 values is 7?pristine?<599?5B?<1589?4B?<4492?3B2?<4983?1B?<9024?3B1?<9393?2B1??10139 a.u.?2B2?.3.Aluminum nitride nanotubes?AlNNTs?doped by the excess electron,e@AlNNT and M@N-AlNNT?M=Li,Na,K?,have been designed and their geometrical,electronic,and nonlinear optical?NLO?properties have been explored theoretically.The results showed that the excess electron narrows the energy gap between HOMO and LUMO values(EH-L)of the doped systems in the range of 3.425.37 eV,which is due to a new energy level HOMO formed for the doped excess electron,with higher energy than the original HOMO of AlNNT.Importantly,the doped excess electron considerably increases the first hyperpolarizability??0?from 130 a.u.of the undoped AlNNT to 646 a.u.for e@AlNNT,2606 a.u.for Li@N-AlNNT,while 1.14×105 a.u.for Na@N-AlNNT,and1.37×106 a.u.for K@N-AlNNT.The enormous large?0 values for Na@N-AlNNT and K@N-AlNNT are attributed to the low transition energy.These results demonstrate that AlNNTs is a promising material in high-performance NLO nanomateria for electronic device.4.The structural,electronic and nonlinear optical properties of alkali metal M?M=Li,Na,K?doped C20F18?NH?2C20H18?DC?were investigated.The results showed that the doping of alkali metals into C20H18 cage?DC@M?M=Li,Na,K??enlarged the?0 of the systems,and?0 increased from 136 a.u.of the undoped structure to 426439 a.u.of DC@M?M=Li,Na,K?.For alkali metal doped outside of the cage?DC····M?M=Li,Na,K??,the effect of doping on?0 is considerable.?0 of DC···M?M=Li,Na,K?in the order of 1158?Li?<1339?Na?<6.7×106 a.u.?K?.The?0 of DC···K is 6.7×106 a.u.,which is 4.9×104 times than that of the undoped structure,and 1.0×104 a.u.than that of the structure DC@K?663 a.u.?.It can be seen that the effect of the doping outside of the cage is better than that in the cage.The doping of alkali metal can greatly enhance the nonlinear optical response of C20F18?NH?2C20H18.This work can provide a very important reference for the design of new optical electronic devices with double cages structures. |
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