梯形高聚物PTL导电机理的研究

本文采用EHMO/CO半经验计算方法,以准一维体系对梯形高聚物聚吩噻嗪(简称PTL)本征态及掺杂态电子能带进行了计算,讨论了PTL的导电机理,提出了当掺杂剂为质子酸时的荷电孤子或极化子导电模型及p-型掺杂时的极化子导电模型。     

导电高聚物聚吡啶的电子能带及其结构研究

聚吡啶(简称PPy)易于进行n-型掺杂并使其电导率大大提高,可用于制作高聚物电池的负极,本文将PPy视为准一维体系,采用EHMO/CO方法计算了新合成的导电高分子材料--聚吡啶4种可能构型的电子能带。     

一维〔M（tmp）〕_2ReO_4（M＝Ni、Cu、Pd）聚合物的能带结构

用紧束缚ＥＨＴ晶体轨道方法对一维〔Ｍ（ｔｍｐ）〕_２ＲｅＯ_４（Ｍ＝Ｎｉ、Ｃｕ、Ｐｄ）聚合物进行了能带计算，利用键向量近似方法对能带的结构及组成进行了讨论。结果表明，该类型聚合物具有不同的导电机理，并进一步研究了环平面间的成键性质及转角改变对聚合物导电性能的影响。     

一维[M（tmp）]2ReO4（M=Ni,Cu,Pd）聚合物的能带结构

用紧束缚ＥＨＴ晶体轨道方法对一维［Ｍ（ｔｍｐ）２］２ＲｅＯ４（＝Ｎｉ，Ｃｕ，Ｐｄ）聚合物进行了能带计算，利用键向量近似方法对能带的结构及组成进行了讨论。结果表明，该类型了事物具有不同的导电机理，并进一步研究了环平面间的成键性质及转角改变对聚合物导电性能的影响。     

一维酞菁聚合物的从头算晶体轨道研究

用密度泛函自洽场晶体轨道方法计算了几种一维酞菁聚合物及其取代衍生物的能带结构和电子性质,得到这些聚合物均是半导体.研究发现,聚合方式和共轭程度的差异不仅影响能隙的大小,而且影响能带的形状.取代基对聚合物能带形状的影响不大,但取代基的电子特性对能带的位置高低起到一定的作用.     

给/吸电子基团取代对PPV类电致发光聚合物光电特性的影响

用量子化学的AM1和EHMACC/CO方法计算PPV,MEH-PPV和CN-PPV的电子和能带结构,讨论了烷氧基(-OR)和氰基(-CN)侧基取代对PPV类电致发光聚合物光电特性的影响.计算结果表明:给电子基团(-OR)取代使聚合物的HOCO(最高占据晶体轨道)能级升高,电离势减小,而吸电子基团(-CN)取代使LUCO(最低未占据晶体轨道)能级降低,电子亲和势增大,两者都使聚合物能隙降低,同时使聚合物的导电类型由PPV的p型转变成CN-PPV的n和p兼容型.该结果解释了MEH-PPV和CN-PPV光谱的红移及CN-PPV高的电致发光效率,为设计新型高效的PPV类电致发光聚合物提供了理论基础.     

供体-受体型共轭聚合物电子结构和导电性能的理论设计

以苯并[1,2-c:4,5-c']二[1,2,5]噻重氮和吡嗪并[2,3-g]喹喔啉为电子受体(A),噻吩、噻吩并[3,2-b]噻吩和二噻吩并[2,3-b:2',3'-d]噻吩为电子供体(D),设计了6种D-A型共轭聚合物.采用B3LYP方法,研究了这6种聚合物的几何结构和电子性质.D-A型共轭聚合物的几何结构和电子结构与电子供体和电子受体的性质,特别是与其提供电子和接受电子的能力密切相关.聚合物的能隙主要受键长交替控制,键长交替越小,能隙越窄.所设计的6种聚合物中,p-BBT-TT具有较窄的能隙(0.48 eV)、较小的载流子有效质量和相对较大的能带宽度,具备理论上的良好导电性能,可能是潜在的优良导电聚合物材料.     

层状金属配位聚合物[{MX2(bipy)}n](M=Ni,Cu,Hg;X=F,Cl,Br,I;)bipy=4,4'-bipyridyl)的电子结构和导电机理研究

用紧束缚(EHT)晶体轨道方法对层状金属配位聚合物[{HgX2(bipy)}(a)](X=Cl,Br;bipy=4,4'-bipyridyl)进行了能带结构计算,并利用键向量方法对这一系列聚合物能带特征和成键性质进行了讨论.研究表明,Fermi能级附近的能带主要是金属汞原子和卤素原子及氮原子之间形成的d-pσ*反键和d-pσ成键作用,这两者作用的强弱对导电性起决定作用.本文还对系列聚合物[(HgX(bipy)}n](M=Ni,Cu,Hg;X=Cl,Br;bipy=4,4'-bipyridyl)可能具有的导电机理和规律进行了探讨.     

噻吩高聚物的量子化学研究

本文用LCAO-CO/EHMO方法对噻吩高聚物的类苯结构(Ⅰ)、类等键长结构(Ⅱ)以及类酸结构(Ⅲ)的电子能带、态密度及电荷分布进行了计算。通过对计算结果的分析, 探讨了噻吩高聚物导电机理的有关问题。     

如何讲好聚合物的导电性(Ⅰ)——一维结构材料一般不是电导体

一般来说,由共价单键连接起来的高分子链已经没有了能够自由运动的电子(载流子),加上主要靠范德华力堆砌的聚合物分子之间距离较大,电子云交叠差,载流子的离域运动极为困难,因此聚合物通常是绝缘体。但是,即使像聚乙炔那样具有π键结构、其主链每个碳原子上带有一个导电电子的聚合物也不能导电,这是因为高分子链是一维体系,空间结构维度性决定了其导电性。一维结构的材料具有派尔斯不稳定性,使得即使每个原子都有导电的价电子,它也不会(在低温下)导电,这是一条普遍的物理规律。     

Electronic and Optical Properties of KNbO3,NaNbO3 and K0.5 Na0.5 NbO3 in Paraelectric Cubic Phase：a Comparative First-principles Study

The structural,electronic and optical properties of KNbO 3 (KN),NaNbO3(NN)and K05 Na0.5NbO3(KNN) in paraelectric cubic phase were calculated employing the plane-wave pseudopotential method based on density functional theory (DFT).The calculated electronic structures of the three crystals show similar features in the valence bands and the lower conduction bands.However,the structures in higher conduction bands differ markedly due to the effect of Na and K atoms.The calculated optical properties reveal that the features of optical spectrum at low energy are dominated by the transitions from O2p valence bands to Nb 4d conduction bands and those at high energy are related to the transitions to K 4s4p and/or Na 3s3p states.Moreover,the optical constants of KNN are approximately the average of KN and NN at high energy.Therefore,the optical properties of KNN in high energy region can probably be altered by changing the ratio of Na/K.     

Electronic structure and spectra of tetrathiotetracene and related molecules

The electronic spectra of tetrathiotetracene (TTT) and of its mono- and dipositive ions have been calculated by the Pariser-Parr-Pople (PPP) method. Furthermore, the band polarizations of the first two bands of TTT have been measured. A reasonable band assignment is given using a new set of PPP parameters based on spectral data of a naphthalene derivative containing similar typical weak S-S bond. Other physical parameters as ionization potential, disproportionation energy, S-S bond length and net π-charges are discussed.     

天然橡胶掺杂导电机制的理论研究

绝大多数导电聚合物均具有共轭骨架,因而化学家们认为共轭作用是聚合物导电的先决条件,然而Thakur用I_2处理具有非共轭骨架的聚合物——聚异戊二烯(PI),其电导率提高十几个数量级,达到了10~(-2)～10~(-1)S·cm~(-1),引起了人们的极大关注。相关实验亦报道了基本类似的结果,但对PI的导电机制尚无统一的认识。本文利用EHMO/CO法,通过计算系列模型的二维能带结构,提出了掺杂模型以探讨天然橡胶的导电机制。     

Vibrational spectroscopic investigation of poly(p‐phenylene sulfide)

Poly(p‐phenylene sulfide) (PPS) is an important polymer of engineering interest particularly useful in the electronics and automotive industries. Normal mode analysis including phonon dispersion has been performed to understand completely the vibrational spectra of this polymer. Various characteristic features of the dispersion curves have been reported. Crossing/Repulsion between various pairs of modes at certain phase values have been explained as arising due to internal symmetry in the energy momentum space. The heat capacity is calculated as a function of temperature via density‐of‐states in the range 220–360 K. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2353–2367, 2009     

Experimental (FT-IR, FT-Raman) and theoretical (HF and DFT) investigation and HOMO and LUMO analysis on the structure of p-fluoronitrobenzene

FT-IR and FT-Raman spectra of p-fluoronitrobenzene (FNO(2)C(6)H(4)) have been recorded in the region 4000-100 cm(-1). In this work, the experimental and theoretical spectra of p-fluoronitrobenzene (p-FNBz) are studied. The molecular geometry and vibrational frequencies are calculated in the ground state of molecule using ab initio Hartree-Fock (HF) and DFT (B3LYP and LSDA) methods with 6-31++G(d,p) and 6-311++G(d,p) basis sets. The computed values of frequencies are scaled to yield good coherence with observed values by using suitable factor. The complete assignments are performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The observed and calculated frequencies are found to be in very good agreement. The alteration of vibration bands due to the substitutions at the first and fourth position of the skeletal ring is also investigated from their characteristic region of linked spectrum. A study on the electronic properties, such as absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, are performed by time dependent DFT (TD-DFT) approach. The electronic structure and the assignment of the absorption bands in the electronic spectra of steady compounds are discussed. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The thermodynamic properties of the title compound at different temperatures have been calculated in gas phase, revealing the correlations between standard heat capacities (C) standard entropies (S), standard enthalpy changes (H) and temperatures.     

Electronic, linear, and nonlinear optical properties of III-V indium compound semiconductors

We have made an extensive theoretical study of the electronic, linear, and nonlinear optical properties of the III-V indium compound semiconductors InX (X=P, As, and Sb) with the use of full potential linear augmented plane wave method. The results for the band structure, density of states, and the frequency-dependent linear and nonlinear optical responses are presented here and compared with available experimental data. Good agreement is found. Our calculations show that these compounds have similar electronic structures. The valence band maximum and the conduction band minimum are located at Gamma resulting in a direct energy gap. The energy band gap of these compounds decreases when P is replaced by As and As by Sb. This can be attributed to the increase in bandwidth of the conduction bands. The linear and nonlinear optical spectra are analyzed and the origin of some of the peaks in the spectra is discussed in terms of the calculated electronic structure. The calculated linear optical properties show very good agreement with the available experimental data. We find that the intra-and interband contributions of the second-harmonic generation increase when moving from P to As to Sb. The smaller energy band gap compounds have larger values of chi(123) ((2))(0) in agreement with the experimental measurements and other theoretical calculations.     

A re-investigation of the electronic spectrum of perylene

A detailed spectroscopic analysis of the electronic absorption spectrum of the perylene molecule in boric acid glass is reported in the region 190–500 nm. To interpret the observed spectrum, the electronic energy levels and oscillator strengths have been calculated using the Free Electron Molecular Orbital (FEMO) method with limited configuration interaction [N.S. Ham and K. Ruedenberg, J. Chem. Phys. 25, 1, 13 (1956)]. The effect of solute concentration on the relative intensities of the absorption bands has also been studied. The experimentally observed transition energies of four strong bands show a linear relationship with the theoretically calculated ones. Agreement between experimental and theoretical results is good.     

聚偏二氟乙烯晶体的电子结构和光学性质

利用含Tkatchenko-Scheffler(TS)色散修正的密度泛函理论的第一性原理方法对九种聚偏二氟乙烯(PVDF)晶相的电子结构和光学性质进行了计算. 结果表明,PVDF晶体作为一种绝缘体,能带具有密集且平直等特征,其带隙值在6.05-7.34 eV之间,且和实验值接近. 价带主要是F原子的2s和2p态起主要贡献,导带主要由C原子的2p态和H原子的1s态共同参与构成. 在0-35 eV光子能量范围内,介电函数、吸收率、反射率和折射率等光学性质发生变化主要在深紫外区域. 根据介电函数等光学参数的谱特点,可以将九种PVDF的晶相划分为{Ⅰ_p},{Ⅱ_pu},{Ⅱ_au,Ⅱ_ad,Ⅱ_pd,Ⅲ_pu},{Ⅲ_au,Ⅲ_ad,Ⅲ_pd}等四类,每一类都具有相似的光学参数特点.     

Geometry and electronic structure of rhombohedral C60 polymer

Geometry and electronic structure of the rhombohedral C₆₀ polymer are studied by means of density-functional theory (DFT) within the local-density-approximation (LDA). It is found that stacking sequence proposed by Chen et al. is more stable than the original model by Núñez-Regueiro et al., although the energy difference between the two is very small. The material is a semiconductor with the LDA gap of 0.68 eV. Conduction bands show dependence on the way of stacking, and density of states has a sharp peak at the conduction bottom. Bond lengths are also calculated and found to be in good agreement with the results of the X-ray structure analysis.