1,3-取代方酸衍生物非线性光学性质的从头算和半经验方法的比较研究

利用从头算HF方法在6 31G 基组水平下,全优化计算了1,3 取代方酸衍生物体系Sq1～Sq12的分子 几何和优化构型下的电子结构.以优化后的构型为基础,应用CIS/6 31G 方法计算了电子光谱.同时应用从头算 CPHF/6 31G 方法和半经验FF/AM1、FF/PM3、FF/MNDO有限场方法计算了分子的二阶非线性光学系数,并对 这四种计算方法的结果进行了系统的比较.结果表明,1,3 取代方酸衍生物的二阶非线性光学系数(β0)受五员 杂环的影响较大,引入吡咯、噻唑和口恶唑五员杂环能提高其β0,含两个杂原子的五员环与方酸碳四员环相连的位 置对β0也有很大的影响.     

具有不同取代基团的香豆素系列分子二阶非线性光学性质的DFT研究

本文设计了具有不同取代基团的7-苯乙烯基香豆素和4-苯乙烯基香豆素的A、B两个系列共14个化合物分子.采用密度泛函理论B3LYP/6-31G方法对其几何构型进行了全结构优化.在所得优化结构的基础上对这些分子的稳态二阶非线性光学(NLO)系数β值进行计算分析,同时用含时密度泛函理论(TD-DFT)对这些分子的电子性质进行了研究.结果表明:此类香豆素化合物具有较大的分子β值,其中A类分子的共面性好,共轭链长,β值均比B类分子的大.14个化合物中前线分子轨道能级差越小的化合物,其βwt值越大.各分子前线分子轨道跃迁对二阶NLO效应有明显的贡献.     

具有不同取代基团的香豆素系列分子二阶非线性光学性质的DFT研究

本文设计了具有不同取代基团的7-苯乙烯基香豆素和4-苯乙烯基香豆素的A、B两个系列共14个化合物分子。采用密度泛函理论B3LYP/6-31G方法对其几何构型进行了全结构优化．在所得优化结构的基础上对这些分子的稳态二阶非线性光学（NLO）系数β值进行计算分析,同时用含时密度泛函理论（TD-DFT）对这些分子的电子性质进行了研究．结果表明：此类香豆素化合物具有较大的分子β值,其中A类分子的共面性好,共轭链长,β值均比B类分子的大．14个化合物中前线分子轨道能级差越小的化合物,其βtot值越大．各分子前线分子轨道跃迁对二阶NLO效应有明显的贡献．     

香豆素衍生物分子二阶非线性光学效应理论研究

用ＣＮＤＯ／Ｓ－ＣＩ程序，计算了了系列香豆素衍生物的分子二阶极化率。从微观上探讨了该类化合物的取代基的电子性质，取代基位置及取代数目对分子二阶极化率的影响。认为取代基的电子性质和取代方式对非线性光学系数有明显的影响。     

DFT研究给/吸电子取代基对D-π-A型苯并噻唑衍生物光电性质及非线性光学性质的影响

采用密度泛函理论(DFT)B3LYP方法计算了苯并噻唑及其三种D-π-A型衍生物的电子结构、电子光谱及重组能,同时结合有限场(FF)方法计算了它们的二阶非线性光学系数βtol值,从而探索取代基与分子的电荷分布、电子光谱及非线性光学性质的关系.计算结果显示,在母体分子的2,5位同时引入给/吸电子基团,2位碳原子的电荷布居发生较大变化,且分子的HOMO能级升高,LUMO能级降低,能隙减小,吸收和发射光谱发生显著的红移,增大了二阶非线性光学系数βtol.随着取代基吸电子能力的增强,分子的电子重组能逐渐变大,而空穴重组能的变化却不大,同时分子的偶极矩有所增加,有利于产生二阶非线性光学活性.     

DFT研究给/吸电子取代基对D-π-A型苯并噻唑衍生物光电性质及非线性光学性质的影响

采用密度泛函理论(DFT) B3LYP方法计算了苯并噻唑及其三种D-π-A型衍生物的电子结构、电子光谱及重组能,同时结合有限场(FF)方法计算了它们的二阶非线性光学系数βtol值,从而探索取代基与分子的电荷分布、电子光谱及非线性光学性质的关系。计算结果显示,在母体分子的2,5位同时引入给/吸电子基团,2位碳原子的电荷布居发生较大变化,且分子的HOMO能级升高,LUMO能级降低,能隙减小,吸收和发射光谱发生显著的红移,增大了二阶非线性光学系数βtol。随着取代基吸电子能力的增强,分子的电子重组能逐渐变大,而空穴重组能的变化却不大,同时分子的偶极矩有所增加,有利于产生二阶非线性光学活性。     

共轭链长及羰基位置对分子二阶极化率的影响

采用引入外场微扰的ＣＮＤＯ／Ｓ－ＣＩ方法，计算一系列二苯基烯酮类化合物的分子二阶极化率（或二阶非线性光学指数）γβｖｃｃ值选取了苯环上含不同取代基团的化合物，从羰基在共轭链中的位置及共轭链长度方面，探讨了其微观二阶非线性光学效应的变化规律，结果表明，共轭链中羰基位置对βｖｃｃ值得重要的影响，并且呈现出一定的规律性，对于苯环上取代相同基团的化合物，其分子二阶非线性光学系数随共轭链长度的变化成指数关系     

吐昔烯衍生物分子的电子光谱与非线性光学性质北大核心CSCD

采用含时密度泛函理论（TDDFT）B3LYP对5个吐昔烯及其衍生物分子的吸收光谱进行理论计算．结果表明,该5个分子的吸收波长在281～307nm范围内,属于近紫外区．使用有限场（FF）方法理论计算5个化合物分子的非线性光学（NLO）性质．结果显示,吐昔烯分子引入烷氧基将明显增大二阶和三阶非线性光学性质（β0和Y值）,此类化合物分子的三阶非线性光学性质明显优于二阶非线性光学性质．     

分子一阶超极化率溶剂效应的理论研究

基于一维谐振子模型建立了极性溶剂对光学二阶非线性分子一阶超极化率产生影响的简化理论模型,推导出了非线性分子的线性极化率α和一阶超极化率β的表达式. 以对硝基苯胺为例,所建立的理论模型计算结果较好地解释了实验获得的溶剂极性对其分子线性吸收峰波长（λ_p）和β值的影响. 关键词： 二阶非线性 溶剂效应 谐振子     

α、β-并三噻吩衍生物分子的二阶非线性光学性质

采用密度泛函理论B3LYP/6-31+g(d)方法对二聚α、β-并三噻吩衍生物的18个分子(a~j2)进行几何构型优化,对其最优构型采用TD-DFT(TDB3LYP/6-31+g(d))计算电子吸收光谱,用有限场FF方法及自编程序计算二阶非线性光学(NLO)性质。计算结果表明,增加共轭链的含乙烯桥的二聚并三噻吩比不含乙烯桥者,βμ(或β0)大1.6—5.3倍;在含乙烯桥二聚α、β-并三噻吩分子(母体分子)末端引入含C=C或C≡C的基团(如-C≡CH与-C=C(CN)_2),比引入强供电子基团(如-N(CH_2CH_3)_2)、单纯吸电子基(如F原子)βμ(或β0)更大;尤其是端接-C=C(CN)2基团的二聚α、β-并三噻吩衍生物,其βμ(或β0)值为104数量级个原子单位(10-29esu),与母体分子相比βμ增大4.8~19.6倍,更有利于改善体系的二阶非线性光学性质,从而可获得良好的非线性光学材料.     

Local approach to polarizabilities and trends in the Raman spectra of semiconductors

The Raman spectra of several II-VI and III–V compounds are well described with one parameter, namely the ratio of non-linear intra-ionic polarizabilities of the individual ions. This approach is justified by the open-shell electronic configuration of the compounds and is based on a simple overlap shell model which reproduces the phonons in many binary compounds. The relations to bond polarizabilities and the anomalous case of oxides are discussed.     

Molecular multipoles and (hyper) polarizabilities from the Buckingham expansion:revisited

The Buckingham expansion is important for understanding molecular multipoles and (hyper) polarizabilities. In this study, we give a complete derivation of the Buckingham expansion in the traced form using successive Taylor series. Based on the derivation results, a general Buckingham expansion in the traced form is proposed, from which highly accurate numerical calculations using the finite field method can be achieved. The transformations from the traced multipoles and multipole-multipole polarizabilities to the corresponding traceless counterparts are realized with an auxiliary traced electric field gradient. The applications of thefinite field method in this study show good agreements with previous theoretical calculations and experimental measurements.     

二阶可降阶微分约束系统的形式不变性

研究具有二阶可降阶微分约束的力学系统的形式不变性．采用两种方法：一是用不可降阶微分约束系统的方法；另一是用降阶后系统的方法．研究两种方法之间的关系．结果表明，用后一种方法可能会失掉一些对称性． 关键词： 约束力学系统 微分约束 降阶 形式不变性 守恒量     

手性分子2, 3-丁二醇的旋光拉曼光谱研究

本文从拉曼峰和旋光拉曼峰出发,通过键极化率和微分键极化率分析研究(2R, 3R)-2, 3-丁二醇. 通过分子C₁和C₂两种点群的优化结构,获得不依赖于这两种结构的结果 和有关这个手性系统物理图像的丰富信息.对分子拉曼键极化率分析,得出在拉曼弛豫过程中, 电荷主要从外围流向骨架结构.对分子微分键极化率的分析,显示在不对称C原子和与其相联系的H原子 两侧化学键, C-O和C-CH₃的微分键极化率的符号正好相反,意味着这个分子具有相当好的手性 不对称性质.对比对称和反对称的键极化率、微分键极化率,本文得到这样的结论: 对于(特别是键伸缩的)键极化率,(大体上是)对称的大于反对称的; 而对于微分键极化率则是反对称的大于对称的. 关键词： 旋光拉曼 键极化率 微分键极化率 2,3-丁二醇     

Spectra of direct excitation of phosphorescence in an isotopic mixed naphthalene crystal

Distributed polarizabilities of a series of n-alkanes C _n H_2n+2 (n = 2-7) in various conformations have been determined using Bader's topological theory of atoms in molecules. Using an appropriate localization scheme, a simple distributed model is constructed, where the methyl and methylene groups are characterized by their dipole polarizability tensors in local frames, and all charge flow polarizabilities between them are retained. A set of average polarizability parameters is proposed that takes into account the local environment of the methyl and methylene groups, and that not only reproduces the polarizability tensor for any member of the n-alkane series in an arbitrary conformation, but also is suitable for the calculation of induction energies.     

Polarizabilities and excitation energies from the multiplicative Kohn-Sham (MKS) approach

The conventional Kohn-Sham expressions for the static isotropic polarizability and vertical excitation energy are evaluated using Kohn-Sham orbitals and eigenvalues determined directly from theoretical electron densities. For a series of small molecules, polarizabilities determined from wavefunction-based BD(T) electron densities differ, on average, by about 2% from conventional BD(T) polarizabilities when the LDA exchange-correlation integrand is used in the electric Hessian matrix. Also polarizabilities determined from Kohn-Sham densities, using the B97-2 hybrid functional, are close to the conventional B97-2 values. To quantify the dependence on the choice of exchange-correlation integrand, calculations are performed also using the HCTH integrand. Rydberg excitation energies determined from BD(T) and B97-2 densities exhibit errors due to inaccuracies in the asymptotic exchange-correlation potential. This category of excitation energy is relatively insensitive to the choice of exchange-correlation integrand; valence excitations can be more sensitive.     

(n*)6-Dependence of tensor polarizabilities of 6snd 1 D 2 Ba Rydberg states

Tensor polarizabilities of levels of the 6snd¹D₂ Rydberg series between n=15 and n=22 were measured by quantum beat spectroscopy. The tensor polarizabilities depend on the sixth power of the effective principal quantum number, which can be explained by a simple theoretical consideration.     

General order imaginary time correlation functions and imaginary frequency susceptibilities

Certain periodicity properties of general order imaginary time (‘temperature’) correlation functions can be used to represent the n + 1th order van der Waals pair interactions as a multiple Fourier series whose coefficients are nth-order imaginary frequency susceptibilities of the two molecules. This representation is a generalization to higher orders of the standard expression for the second-order van der Waals pair interaction in terms of imaginary frequency polarizabilities. The fourth-order dispersion energy for spherical molecules in their ground state is obtained as a sum of multiple integrals over imaginary frequencies of certain products of dynamic linear and cubic polarizabilities of the two molecules.     

Measurement of the proton spin polarizabilities at MAMI

The spin polarizabilities of the nucleon are fundamental structure constants which describe the response of the nucleon spin to an incident polarized photon. The most model-independent way to measure the nucleon spin polarizabilities is the Compton scattering with polarization degrees of freedom. Three Compton scattering asymmetries on the proton were measured in the Δ(1232) region using a polarized incident photon beam and a polarized (or unpolarized) proton target at the Mainz Microtron (MAMI). These asymmetries are sensitive to values of the spin polarizabilities. Fits to asymmetry data were performed using a dispersion model calculation, and a separation of all four proton spin-polarizabilities in the multipole basis was achieved. The values of the proton spin polarizabilities are presented.