基于密度泛函理论的外电场下C_3F_8微观特性的研究

全氟丙烷(C_3F_8)作为一种拥有较低温室效应的SF_6替代气体,被国内外学者广泛研究.为了从分子层面上揭示全氟丙烷在外电场作用下微观特性的变化情况,采用密度泛函理论中的M06-2X方法,在6-31G(d)基组水平上优化得到了C_3F_8的基态稳定构型.分析了不同外电场(0-0.020 a.u.)对C_3F_8分子的结构、Highest Occupied Molecular(HOMO)、Lowest Unoccupied Molecular(LUMO)、能隙、键级的影响,并研究了全氟丙烷分子的激发态能、波长、振子强度.结果表明,在所加电场范围内,随着电场强度的增大,C_3F_8分子最高占据轨道能级逐渐增大,最低空轨道能级逐渐减小,能隙E_G逐渐减小, C_3F_8分子的化学活性增强;C_3F_8分子中的C-C键的Mayer Bond Order (MBO)值随电场强度的增大均出现增大的情况,分子的稳定性降低;C_3F_8分子激发态的激发能总体上呈现出减小的趋势,激发态的波长总体上则呈现出增大的趋势,表明在外电场的作用下,全氟丙烷分子变得越来越容易激发.     

外电场下C_4F_7N分子的结构与特性

C_4F_7N作为优质的SF_6环保型替代气体而备受关注.为了研究外电场对C_4F_7N分子结构和性能的影响,本文采用密度泛函明尼苏达M06-2X方法分别在6-311g(d,p)基组和aug-cc-pVTZ基组水平上对C_4F_7N分子进行优化,分析了不同外电场(0-0.040 a.u., 1a.u.=5.142×10~(11) V/m)作用下分子的结构和能量变化,外电场对分子红外光谱、ADCH电荷、偶极矩以及极化率的影响.研究结果表明:随着电场的增强,分子各键长均发生变化,其中R(1,4)、R(4,5)、R(1,12)、R(2,7)变化明显,R(1,4)、R(4,5)键长逐渐伸长,R(1,12)、R(2,7)键长逐渐缩短,分子总能量降低,偶极矩和极化率升高,C_4F_7N分子稳定性随着电场的增强而降低;分子红外光谱高频区吸收峰较为密集,且既有红移也有蓝移;ADCH原子电荷发生显著变化.     

基于密度泛函理论的外电场下C_3F_8微观特性的研究

全氟丙烷(C_3F_8)作为一种拥有较低温室效应的SF6替代气体，被国内外学者广泛研究.为了从分子层面上揭示全氟丙烷在外电场作用下微观特性的变化情况，采用密度泛函理论中的M06-2X方法，在6-31G(d)基组水平上优化得到了C_3F_8的基态稳定构型.分析了不同外电场(0-0.020 a.u.)对C_3F_8分子的结构、Highest Occupied Molecular(HOMO)、Lowest Unoccupied Molecular(LUMO)、能隙、键级的影响，并研究了全氟丙烷分子的激发态能、波长、振子强度.结果表明，在所加电场范围内，随着电场强度的增大，C_3F_8分子最高占据轨道能级逐渐增大，最低空轨道能级逐渐减小，能隙EG逐渐减小，C_3F_8分子的化学活性增强; C_3F_8分子中的C-C键的Mayer Bond Order (MBO)值随电场强度的增大均出现增大的情况，分子的稳定性降低; C_3F_8分子激发态的激发能总体上呈现出减小的趋势，激发态的波长总体上则呈现出增大的趋势，表明在外电场的作用下，全氟丙烷分子变得越来越容易激发.     

基于密度泛函理论的外电场下C_5F_(10)O的结构及其激发特性

采用密度泛函(DFT)B3LYP/6-311g(d)对C_5F_(10)O分子进行几何结构优化,研究外加电场(0-0.03 a.u.,1 a.u.=5.142×10~(11) V/m)对分子的几何结构、能量、前线轨道能级、红外光谱的影响.在相同基组下,采用TD-DFT方法计算和分析C_5F_(10)O的轨道成分和激发特性.研究表明:随着电场增加, 5C—15F与4C=16O键能逐渐减小,键长增大; 13F原子的电荷布居数变化最快,更容易在外电场力的作用下失去电子;分子体系势能不断增加,稳定性逐渐减低;能隙E_G值不断减小,分子更容易激发到激发态参与到化学反应中.红外光谱中, 4个吸收峰发生蓝移, 4个吸收峰发生了红移.使用空穴-电子分析法,指认了C_5F_(10)O分子前8个单重激发态的激发特征.第一激发态的激发能微小增长,波长减小,出现蓝移;其余激发态的激发能均降低,波长均变长,发生红移,导致C_5F_(10)O分子中的电子变得越来越容易激发,体系的稳定程度减小.     

外电场作用下C_6F_(12)O分子的结构和激发态

采用明尼苏达密度泛函(M06-2X)在6-31G(d)的基组水平上对C_6F_(12)O分子在不同外电场强度(0.000a.u.～0.040a.u.)下进行了计算。分析了不同外电场下基态的分子结构、原子电荷布居、偶极矩、分子总能量。然后利用TD-DFT方法研究了各电场下C_6F_(12)O分子的激发态激发能、波长、振子强度和紫外-可见吸收光谱(UV-vis)。结果表明分子的基态和激发态性质与外电场呈依赖关系。随着外电场的增强,分子总能量逐渐减小,偶极矩增大。分子的激发态能总体上减小,C_6F_(12)O分子变得容易激发。C_6F_(12)O分子由基态跃迁到激发态光子吸收波长总体增大,且主要集中在紫外区域。激发态的振子强度部分增加部分减少,变化复杂。UV-vis光谱随着外电场的增加,在无外电场时曲线上132 nm和162 nm出现的2处吸收峰均发生红移。     

外电场作用下CHCl_3分子的特性研究

采用密度泛函B3LYP方法在6-31G(d)基组水平上,优化得到CHCl3分子在不同外电场下(-0.04~0.04a.u.)的基态稳定构型、偶极矩、HOMO能级、LUMO能级、能隙、电荷分布、谐振频率和红外光谱强度。结果表明,分子结构、电荷分布与外电场有着强烈的依赖关系,当电场由F=0.024 3a.u.变到F=0.024 4a.u.时,Cl原子由电正性向电负性转变;随着正向电场的增大,HOMO能级、LUMO能级和能隙都先增大后减小,分子偶极矩随正向外电场的增大先减小后增大,当F=0a.u.时能隙取最大值EG=7.238 19eV,当F=-0.02a.u.时偶极矩取最小值μ=0.086 7Debye,同时,外电场对CHCl3分子的激发能、振子强度和红外光谱的位置和强度均有一定影响。     

外电场对ZrH2(ZrD2,ZrT2)固溶体热力学函数的影响

采用Gaussian03程序及密度泛函(B3P86)方法,对Zr原子利用外部基函数8s7p3d,对H2(D2,T2)利用6-311g**全电子基函数,优化了在外电场作用下ZrH2分子微观结构,研究了锆与氢同位素气体反应的热力学函数及氢同位素平衡压力随温度和外电场的变化关系.研究表明:随着正向电场的增加,分子微观结构及其气体平衡压力发生明显变化.在293.16K,外电场从-0.004 a.u.到0.004 a.u.变化时,氢平衡压力相差六个数量级.说明外电场对金属氢化物的热力学函数具有一定的影响.     

基于密度泛函理论的外电场下双酚A型环氧树脂分子的结构及特性

采用密度泛函m062x的方法在6-31g(d)基组上对双酚A型环氧树脂分子进行优化得到了它的稳定结构,并且研究了不同外电场(0-0.013 a.u., 1 a.u.=5.142×10~(11) V/m)作用下双酚A型环氧树脂分子的分子结构、电偶极矩和分子总能量,偶极矩、极化率、前线轨道的能级和成分,原子之间的键能和红外光谱的变化.研究表明:随着外加电场的增大,双酚A型环氧树脂分子从倒V型结构逐渐变成线性结构,总能量降低,偶极矩和极化率都升高,且双酚A型环氧树脂分子的稳定性随着外加电场的增大而降低;最高占据轨道能级随着外加电场的增大而增大,沿逆电场方向分子链端表现出亲核反应活性,最低空轨道能级随着外加电场的增大而减小,沿电场方向分子链端表现出亲电反应;位于分子两端环氧基团上的C-C,C-O容易发生断裂,进而破环了双酚A型环氧树脂分子的稳定性;分子红外光谱在高频区的吸收峰出现了明显的红移现象.     

基于密度泛函理论的外电场下双酚A型环氧树脂分子的结构及特性

采用密度泛函m062x的方法在6-31g(d)基组上对双酚A型环氧树脂分子进行优化得到了它的稳定结构,并且研究了不同外电场(0-0.013 a.u.,1 a.u.=5.142×10~(11)V/m)作用下双酚A型环氧树脂分子的分子结构、电偶极矩和分子总能量,偶极矩、极化率、前线轨道的能级和成分,原子之间的键能和红外光谱的变化.研究表明:随着外加电场的增大,双酚A型环氧树脂分子从倒V型结构逐渐变成线性结构,总能量降低,偶极矩和极化率都升高,且双酚A型环氧树脂分子的稳定性随着外加电场的增大而降低;最高占据轨道能级随着外加电场的增大而增大,沿逆电场方向分子链端表现出亲核反应活性,最低空轨道能级随着外加电场的增大而减小,沿电场方向分子链端表现出亲电反应;位于分子两端环氧基团上的CC,C-O容易发生断裂,进而破环了双酚A型环氧树脂分子的稳定性;分子红外光谱在高频区的吸收峰出现了明显的红移现象.     

基于密度泛函理论的外电场下盐交联聚乙烯分子的结构及其特性

交联聚乙烯是主要的高压电缆绝缘材料.为了研究外电场对盐交联分子结构的影响,本文对Zn原子使用def2-TZVP基组, C, H, O原子使用6-31G(d)基组,运用明尼苏达密度泛函(M06-2X)对交联聚乙烯分子进行优化得到了它的稳定结构.并研究了不同外电场(0—0.020 a.u., 1 a.u.=5.142×10~(11)V/m)作用下盐交联聚乙烯分子结构和能量变化,外电场对前线轨道的能级和成分的影响,原子之间的键级、断键和红光光谱的变化.研究结果表明:随着电场的增大,交联聚乙烯分子从空间网状结构逐渐变成线性结构,总能量降低,但势能增大,偶极矩和极化率升高,交联聚乙烯分子的稳定性随着电场的增大而降低;最高占据轨道能级持续增大,最低空轨道能级从0.011 a.u.电场开始持续降低,能隙持续降低,临界击穿场强为11.16 GV/m;沿电场方向聚乙烯链端表现出亲核反应活性,它的C—C键更容易断裂,形成甲基碳负离子,逆电场方向聚乙烯链端表现出亲电反应活性,它的C—H键更容易断裂形成H正离子;分子红外光谱高频区吸收峰明显红移,低频区吸收峰既有红移又有蓝移.     

Predicting the reaction mechanism of nucleophilic substitutions at carbonyl and thiocarbonyl centres of esters and thioesters

In nucleophilic substitution reactions at carbonyl centres, there are two possible channels. The first one occurs when the attack of nucleophilic agents takes place simultaneously with the departure of the nucleofuge. This process is named as concerted. The second possibility is the formation of a reaction intermediate, typically a tetrahedral intermediate from which the nucleofuge departs after passing through a second transition state. This second mechanism is defined as stepwise. Whether a concerted or stepwise mechanism is to be expected for a given reaction depends on several factors. Among these determinants are the nucleophilicity of the attacking group, the leaving group ability of the nucleofuge, and the solvent, which affects both the stability of the intermediate or the transition states involved. The role of the electrophilic centre can however become an important factor that can determine the reaction mechanism. In this work we show that the group nucleophilic Fukui function model may be used to rationalize and to predict the reaction mechanism of the title compounds towards alicyclic amines. In general, when the electrophilic carbon centre is attached to the soft sulfur atom, the reaction mechanism is predicted to follow a stepwise route. When the electrophilic carbon atom is attached to a harder oxygen centre, the reaction mechanism is determined by chemical substitution at the nucleofuge moiety. Experimental verification for a set of four substrates is presented. Copyright © 2012 John Wiley & Sons, Ltd.     

F+HCl/DCl反应散射的量子含时波包

在Deskevich等人最近构建的势能面上，利用量子含时波包方法，研究了F+HCl/DCl的反应散射动力学．在总角动量J=0的情况下，得出了这两个反应具有不同初始振转态条件下的总反应几率．计算结果表明，对于这两个反应，反应物的转动激发态可以明显的提高反应几率，对于F+HCl反应这种提高尤其明显．而振动激发只是对降低碰撞能反应阈值有帮助，对总的反应几率几乎没有任何影响．另外，这两个反应的进行途径有明显的转动自由度部分．在含有较轻的氢原子的F+HCl反应中，总反应几率中所呈现的量子共振和隧穿效应较之F+DCl     

金红石TiO2晶体中F型色心电子结构及其吸收光谱研究

运用Ｆ型色心的类氢离子波函数结合电荷自洽离散变分法,对ＴｉＯ２晶体中Ｆ型色心的电子结构进行了计算,并利用能量最小原理优化了色心格点周围的Ｔｉ,Ｏ离子结构,得到了ＴｉＯ２晶体中Ｆ,Ｆ＋和Ｆ＾２＋心的能带、态「密度,并讨论了色心的光学跃迁模式,计算结构表明,Ｆ,Ｆ＾＋心在ＴｉＯ２晶体的禁带中引入的旋主能级,Ｆ＾２＋心在禁带中引入了浅受主能级,Ｆ和Ｆ＋心的光学跃有分别是０．８５ｅＣ,１．６７ｅＣ,经还原     

利用延迟荧光光谱F730/F685的逆境胁迫生理检测方法

以玉米98-2为样品,实验分析了高温、盐及紫外UV-B胁迫下,样品离体叶片延迟荧光发射光谱的变化.标记685 nm主峰带的最高峰值为F685,730nm次峰带的最高峰值为F730,实验发现不同的逆境胁迫对比值F730/F685均产生了显著的影响.结合样品在相同逆境下叶绿素荧光参数Fv/Fm以及DF强度的检测实验,结果表...     

A comparison of the scalar Hermitian product versus the complex product for obtaining electron densities and Fukui functions from complex wavefunctions for the temporary anion resonance states of Be−, Mg− and Ca−

ABSTRACT

Densities and Fukui functions using the complex product, c-product (f|g) and the scalar Hermitian product <f|g> are compared for two ²P resonance states of Be^?, the ²P resonance state of Mg^? and the ²D resonance state of Ca^?. Use of the c-product has been shown to be necessary when analysing the complex eigenfunctions of a complex-scaled Hamiltonian. The c-product produces complex electron densities from complex wavefunctions, but only the real part is used for the Fukui functions. The real part of the density matrix obtained using the c-product doesn’t satisfy the Pauli principle, and can produce negative regions in the electron densities. The Fukui functions and densities obtained using the c-product compare well with the Fukui functions and densities obtained using the scalar Hermitian product.     

Impact of ketone and amino on the inner shell of guanine

Removal of the functional groups of guanine, i.e. ketone and amino, one by one produces model molecules of hypoxanthine, 2‐aminopurine and unsubstituted purine. The impact of the ketone and amino moieties on guanine is revealed using their atomic‐site‐based inner‐shell electronic properties and spectra. A density functional theory based model has been employed to study the model molecules. Electronic properties, such as Hirshfeld charges and inner‐shell chemical shift, are found to be both site‐dependent and moiety‐dependent. The site‐based inner‐shell chemical shift of the species exhibits a simple linear correlation, although certain similarities among the model molecules regroup the species into two pairs of purine and 2‐aminopurine, as well as hypoxanthine and guanine.     

梯形化合物NaV2O4F电子结构的第一性原理研究

采用基于密度泛函理论(DFT)的第一性原理赝势平面波方法, 通过自旋极化的广义梯度近似(GGA)电子结构计算对梯形化合物NaV2O4F进行了研究. 考虑了四种假想的自旋有序态, 计算结果表明该化合物的磁基态具有二维反铁磁(AFM)结构, 即沿梯阶和梯腿方向都表现为AFM作用. 能带结构显示NaV2O4F为绝缘体材料, 带隙约为1.0 eV. 方锥体中的晶体场劈裂使得VO4F方锥体中的 V4+(3d1)离子的未配对电子填充dxy轨道. 电负性极强的F离子使得梯阶上的共价性减弱,并导致梯阶上的交换作用减弱. 采用Noodleman的对称性破缺方法由Ising模型拟合出的自旋交换耦合常数表明NaV2O4F的梯间还存在强度与梯阶的AFM作用相当的铁磁(FM)相互作用, 说明该梯形化合物很可能不是一种自旋梯材料.     

29Si and 19F MAS NMR spectra of isolated 29Si(19F)2 and 29Si(19F)3 spin systems: experiments and simulations

We consider ²⁹Si and ¹⁹F MAS NMR spectra of isolated ²⁹Si(¹⁹F)₂ and ²⁹Si(¹⁹F)₃ spin systems in two organosilicon compounds of the type RR’SiF₂ and RSiF₃(R,R′=organic ligands). Experimental spectra are analysed by means of numerical simulations. It is found that the SiF₃ group in RSiF₃ is reorienting rapidly around the molecular Si–C bond direction in the solid state. The two ¹⁹F shielding tensors in RR’SiF₂ have strongly differing orientations relative to the two Si–F bond directions in the molecule. Possibilities and limitations of straightforward MAS NMR approaches for the full characterisation of ²⁹Si(¹⁹F)₂ and ²⁹Si(¹⁹F)₃ spin systems and other dipolar coupled two and three-spin systems are discussed.     

Theoretical study of the Ru + CH3F reaction

CASSCF-MRMP2 calculations have been performed to analyse the reaction of fluoromethane with a bare ruthenium atom. Potential energy curves emerging from the ground state and the first excited state of the reactants, Ru(⁵F, ³F;d⁷s¹) + CH₃F, were calculated for representative electronic states associated with different approaching modes of the fragments. Whereas no favourable channels correlating with the ground state asymptote were detected for the insertion of the ruthenium atom into the C–H bond of the methyl fluoride molecule, the oxidative addition of the C–F bond of this molecule to the metal atom along the reaction path evolving from the ground state of the fragments leads to the stable inserted product CH₃–Ru–F. Although forming less stable products, insertion of ruthenium into the C–H and C–F bonds of the fluorocarbon molecule can occur through electronic states which emerge from the excited triplet state asymptote.     

The attachment of amino fragment to purine: inner‐shell structures and spectra

The impact of the amino fragment (–NH₂) attachment on the inner‐shell structures and spectra of unsubstituted purine and the purine ring of adenine are studied. Density functional theory calculations, using the LB94/TZ2P//B3LYP/TZVP model, reveal significant site‐dependent electronic structural changes in the inner shell of the species. A condensed Fukui function indicates that all of the N and C sites, except for N₍₁₎ and C₍₅₎, demonstrate significant electrophilic reactivity (f^? > 0.5 in |e|) in the unsubstituted purine. Once the amino fragment binds to the C₍₆₎ position of purine to form adenine, the electrophilic reactivity of these N and C sites is greatly reduced. As expected, the C₍₆₎ position experiences substantial changes in energy and charge transfer, owing to the formation of the C—NH₂ bond in adenine. The present study reveals that the N1s spectra of adenine inherit the N1s spectra of the unsubstituted purine, whereas the C1s spectra experience significant changes although purine and adenine have geometrically similar carbon frames. The findings also indicate that the attachment of the NH₂ fragment to purine exhibits deeply rooted influences to the inner‐shell structures of DNA/RNA bases. The present study suggests that some fragment‐based methods may not be applicable to spectral analyses in the inner shell.