g-CN体系的准粒子能带结构和光学特性（英文）

利用多体格林函数理论,本文研究了二维CN体系(包括triazine和tri-s-triazine)的激发态特性。通过GW方法,我们计算了准粒子的能量。考虑电子-空穴相互作用,通过求解Bethe-Salpeter方程,我们获得了激发态能量和光谱。我们发现,在这两种CN体系的价带中,σ轨道和π轨道之间的交换作用非常强烈。由于占据的σ轨道和π轨道之间的准粒子修正量非常不同,因此,为了得到准确的带隙值和光谱,我们需要对这两种轨道开展精确的GW计算。与单层的CN体系相比,双层结构中层与层之间的范德华相互作用使带隙值降低了0.6 e V,而光吸收谱红移了0.2 e V,这是由于双层结构具有更小的激子束缚能。我们计算的吸收峰的位置与实验结果符合很好。实验中的吸收峰主要是由深能级的π轨道到π*轨道的跃迁形成的。π→π*跃迁和σ→π*跃迁之间的耦合能够在长波长范围产生弱的吸收尾巴,如果调整入射光的极化方向,由σ→π*跃迁产生的高强度的吸收峰将会在更低能量处出现。     

g-CN体系的准粒子能带结构和光学特性

利用多体格林函数理论,本文研究了二维CN体系(包括triazine和tri-s-triazine)的激发态特性。通过GW方法,我们计算了准粒子的能量。考虑电子-空穴相互作用,通过求解Bethe-Salpeter方程,我们获得了激发态能量和光谱。我们发现,在这两种CN体系的价带中,σ轨道和π轨道之间的交换作用非常强烈。由于占据的σ轨道和π轨道之间的准粒子修正量非常不同,因此,为了得到准确的带隙值和光谱,我们需要对这两种轨道开展精确的GW计算。与单层的CN体系相比,双层结构中层与层之间的范德华相互作用使带隙值降低了0.6 eV,而光吸收谱红移了0.2 eV,这是由于双层结构具有更小的激子束缚能。我们计算的吸收峰的位置与实验结果符合很好。实验中的吸收峰主要是由深能级的π轨道到π^*轨道的跃迁形成的。π→π^*跃迁和σ→π^*跃迁之间的耦合能够在长波长范围产生弱的吸收尾巴,如果调整入射光的极化方向,由σ→π^*跃迁产生的高强度的吸收峰将会在更低能量处出现。     

DNA甲基化-非甲基化碱基间堆积作用的理论研究

运用二级Mфller-Plesset(MP2)理论方法和cc-pVDZ基组优化了6-甲基鸟嘌呤(O6-MethylG),4-甲基胸腺嘧啶(O4-MethylT)以及5-甲基胞嘧啶(C5-MethylC)与DNA碱基鸟嘌呤(G),腺嘌呤(A),胞嘧啶(C),胸腺嘧啶(T)之间的堆积构型.在MP2/aug-cc-pVXZ//MP2/cc-pVDZ(X=D,T)水平上,采用完全基组外推方法校正了堆积碱基对间的相互作用能,并用完全均衡校正法(CP)校正了基组重叠误差(BSSE).MP2计算结果表明,DNA碱基甲基化使得嘧啶-嘧啶、嘧啶-嘌呤堆积碱基间的平行旋转角发生明显改变,并使堆积碱基间的相互作用能增大.在MP2/cc-pVDZ计算级别上得到了各堆积碱基对的全电子波函数,并用分子中的原子理论(AIM)分析了堆积碱基对间的弱相互作用.AIM分析结果显示,甲基化增强了堆积碱基间的π-π作用,且甲基氢与相邻碱基间形成H2CH…X(X=O,N,CH3,NH2)等类型的氢键.甲基化损伤使碱基间重叠程度增大、π-π作用增强以及堆积碱基间形成多个氢键,是堆积作用能增加的主要原因.     

尿酸与水的氢键作用研究

尿酸与水的相互作用是进行尿酸和其他物质在水溶液中研究的基础。使用实验与理论计算相结合研究了二者在水溶液中的氢键作用及作用位点。结果表明其作用在本质上是弱氢键到中等强度氢键,且尿酸的主要作用位点为O11和H18。氢键作用的存在使尿酸的n→π~*跃迁吸收带发生蓝移,电化学氧化电位变大。     

有机及金属有机苯乙炔树状分子体系的非线性光学性质的理论研究

应用密度泛函理论研究了一系列有机及金属有机苯乙炔树状分子的激发态性质和非线性光学性质。计算的电子吸收光谱显示这些树状分子均在低能区域有一个最强的吸收;此外,金属有机体系的吸收光谱和有机体系相比发生了明显的红移。响应性质的计算结果表明共轭体系的扩展和金属有机基团的引入都使得苯乙炔树状分子的非线性光学极化率显著增加,尤其是含Ru体系,其β和γ值呈数量级增长。对于有机体系和含Pd体系,发生在共轭体系内部的π→π*电荷跃迁是产生分子一阶和二阶超极化率的主要原因。而含Ru体系相当大的非线性响应则主要起源于Ru的轨道到共轭体系的π*的跃迁,同时与Ru相邻的C≡C到共轭体系的π→π*跃迁起着辅助贡献。     

金属四重键化合物M2X4(PMe3)4(M=Cr,Mo,W;X=F,Cl,Br,I)结构和电子光谱的密度泛函理论研究

采用密度泛函理论方法,在TZ2P-STO基组水平下,对金属四重键化合物M2Cl4(PMe3)4(M=Cr,Mo,W)和Mo2X4(PMe3)4(X=F,Cl,Br,I)的几何结构进行优化,分析了电子结构,并运用TDDFT方法对其低占据激发态进行了计算.考虑相对论效应的ZORA方法能够较好地重现M2X4(PMe3)4的几何结构.M2X4(PMe3)4的电子结构分析表明其d电子的组态为σ2π4δ2,前线轨道能级顺序为πlig<πd/σd<δd<δd*.金属原子和卤素配体的改变虽然使轨道能量发生变化,但没有影响轨道的排布顺序.TDDFT方法对M2X4(PMe3)4δd→δd*和πd→δd*跃迁能量的计算较为准确,对πlig→δd*(LMCT)跃迁能量的计算误差较大.金属原子、卤素配体以及相对论效应对激发能的影响可以根据分子轨道能级的变化给予解释.     

槲皮素与尿嘧啶和胸腺嘧啶氢键的结合位点

深入理解药物分子和核酸碱基间的相互作用机制对合理设计研发新型高效药物有重要意义. 本文运用密度泛函理论B3LYP方法对核酸碱基尿嘧啶和胸腺嘧啶与药物分子槲皮素间的氢键相互作用位点进行了研究. 使用B3LYP/6-31G(d)方法优化得到了30个稳定的氢键复合物结构, 使用B3LYP/6-311++G(3df,2p)方法计算了这些复合物的结合能. 研究结果表明, 槲皮素可以使用5个不同的结合位点与尿嘧啶或胸腺嘧啶形成氢键复合物, 尿嘧啶或胸腺嘧啶可以使用3个不同的结合位点与槲皮素形成氢键复合物. 当槲皮素的结合位点固定时, 槲皮素与尿嘧啶的位点u1或胸腺嘧啶的位点t1形成的氢键作用最强, 与位点u2或位点t2形成的氢键强度最弱; 当尿嘧啶或胸腺嘧啶的作用位点固定时, 二者与槲皮素的位点qu1 形成的氢键作用最强, 与位点qu5 作用强度次之, 与位点qu3的作用强度最弱. 分子中原子(AIM)和自然键轨道(NBO)分析计算结果表明, 轨道作用在氢键中起重要作用.     

双核浆叶式钨配合物电子结构和电子光谱的理论研究

用密度函数理论中的B3LYP方法,对甲脒做配体的过渡金属双核浆叶式配合物W2（form)4((form)^-=[(p-tol)NCHN([p-tol)^-]^-)进行了分子轨道计算,结果表明,W－W键具σ^2π^4δ^2四重键的性质,W－W间的成键和反键分子轨道顺序为σ＜π＜δ＜σ^*＜π^*＜δ^*。用单激发组态相互作用（CIS）方法计算了W2(form)4的电子吸收光谱,得到这种配合物的最低能吸收光谱为λ＝496nm,这是δ（dxy）→σ^*(spz)跃迁产生的,属于金属内部的电荷迁移。     

Ph(SiMe_2)_nPh体系π→π~*UV谱的研究

本文依据Spin-Free理论,使用Gelfand基构造多电子波函数,采用四轨道模型,对Ph(SiMe_2)_nPh体系(n=1～6)的π→π*跃迁进行了EHMO-CI计算,所得第一及第二跃迁能与UV谱的实验结果基本一致。当体系硅链原子数增加时,第一吸收带红移的现象起因于LUMO中d轨道成份增加,导致电子排斥作用变化。在LUMO中,硅链上的d轨道以πd的形式与苯环π~*轨道进行πd—π~*共轭互相作用,这种作用很可能与第一吸收带的强度有内在的联系。     

7-吡啶吲哚同分异体结构与电子光谱性质的理论研究

运用密度泛函理论对7-吡啶吲哚可能存在的构型进行优化,计算异构体的几何构型、电子结构、前线分子轨道;应用含时密度泛函理论计算了异构体b,c和e的电子光谱性质以及溶剂效应对光谱性质的影响.结果表明,溶剂极性的增加使b的电子光谱蓝移,而c和e的电子光谱红移,且溶剂极性对最大吸收波长影响幅度较小.前线分子轨道分析,表明该类化合物的主要吸收光谱主要对应于分子中的HOMO→LUMO电子跃迁,且为π→π*跃迁.     

洛汾碱衍生物的电子结构及光谱性质的理论研究

采用密度泛函理论(DFT)的B3LYP/6-31G*方法,对4种洛汾碱类化合物的几何构型进行了优化,在此基础上计算分子的电子结构,并结合有限场FF方法研究了二阶非线性光学(NLO)性质.用含时密度泛函理论(TD-DFT)对上述化合物分子进行吸收光谱的研究.研究表明在4,5-二-苯基-2-对甲酰苯基咪唑生色团中4,5苯环上引入硝基和3位N原子引入苄基改变分子的共轭平面,使二阶非线性极化率总有效值(βtot)减小,吸收峰总体蓝移.同时还发现,在CH2Cl2溶剂中a和c分子的λmax主要来源于HOMO→LUMO的π一π*跃迁,b和d分子的λmax主要来源于HOMO→LUMO+2的π→π*跃迁.     

Natural bond orbital analysis in the ONETEP code: Applications to large protein systems

First principles electronic structure calculations are typically performed in terms of molecular orbitals (or bands), providing a straightforward theoretical avenue for approximations of increasing sophistication, but do not usually provide any qualitative chemical information about the system. We can derive such information via post‐processing using natural bond orbital (NBO) analysis, which produces a chemical picture of bonding in terms of localized Lewis‐type bond and lone pair orbitals that we can use to understand molecular structure and interactions. We present NBO analysis of large‐scale calculations with the ONETEP linear‐scaling density functional theory package, which we have interfaced with the NBO 5 analysis program. In ONETEP calculations involving thousands of atoms, one is typically interested in particular regions of a nanosystem whilst accounting for long‐range electronic effects from the entire system. We show that by transforming the Non‐orthogonal Generalized Wannier Functions of ONETEP to natural atomic orbitals, NBO analysis can be performed within a localized region in such a way that ensures the results are identical to an analysis on the full system. We demonstrate the capabilities of this approach by performing illustrative studies of large proteins—namely, investigating changes in charge transfer between the heme group of myoglobin and its ligands with increasing system size and between a protein and its explicit solvent, estimating the contribution of electronic delocalization to the stabilization of hydrogen bonds in the binding pocket of a drug‐receptor complex, and observing, in situ, the n → π* hyperconjugative interactions between carbonyl groups that stabilize protein backbones. © 2012 Wiley Periodicals, Inc.     

Theoretical Studies on the Electronic Structures and Spectral Properties of 4,4′-（Ethane-1,2-diylbis-（oxy））dibenzaldehyde and Its Polymorph

The ground state geometries, frontier molecular orbital properties, and absorption properties of 4,4′-(ethane-1,2-diylbis(oxy))dibenzaldehyde (EDO-DBDHD) and its polymorph have been studied theoretically. The density functional theory (DFT) method was employed to optimize the ground state geometries, and theoretical data reveal that EDO-DBDHD features the planar molecular conformations, in contrast to V-shaped structures of its polymorph, which agrees with the experimental data. Additionally, the absorption spectra of both compounds were predicted using time-dependent density functional theory (TDDFT). The calculated results show that the lowest lying absorption bands of these compounds have the transition configurations of HOMO → LUMO, resulting in the transition character of π→π*/n→π*. The transition of HOMO → LUMO+3 mainly contributes to the highest lying absorption bands of two compounds at 225 nm with the character of π→π*/n→π*.     

Theoretical study on the transition-metal oxoboryl complex: M-BO bonding nature, mechanism of the formation reaction, and prediction of a new oxoboryl complex

The Pt-BO bonding nature and the formation reaction of the experimentally reported platinum(II) oxoboryl complex, simplified to PtBr(BO)(PMe(3))(2), were theoretically investigated with the density functional theory method. The BO(-) ligand was quantitatively demonstrated to have extremely strong σ-donation but very weak d(π)-electron-accepting abilities. Therefore, it exhibits a strong trans influence. The formation reaction occurs through a four-center transition state, in which the B(δ+)-Br(δ-) polarization and the Br → Si and O p(π) → B p(π) charge-transfer interactions play key roles. The Gibbs activation energy (ΔG°(++)) and Gibbs reaction energy (ΔG°) of the formation reaction are 32.2 and -6.1 kcal/mol, respectively. The electron-donating bulky phosphine ligand is found to be favorable for lowering both ΔG°(++) and ΔG°. In addition, the metal effect is examined with the nickel and palladium analogues and MBrCl[BBr(OSiMe(3))](CO)(PR(3))(2) (M = Ir and Rh). By a comparison of the ΔG°(++) and ΔG° values, the M-BO (M = Ni, Pd, Ir, and Rh) bonding nature, and the interaction energy between [MBrCl(CO)(PR(3))(2)](+) and BO(-) with those of the platinum system, MBrCl(BO)(CO)(PR(3))(2) (M = Ir and Rh) is predicted to be a good candidate for a stable oxoboryl complex.     

6-N,N-二甲基腺嘌呤激发态结构动力学的共振拉曼光谱

采用共振拉曼光谱技术和密度泛函理论方法研究了6-N,N-二甲基腺嘌呤(DMA)的A带和B带电子激发和Franck-Condon 区域结构动力学. π_H→π_L^*跃迁是A带吸收的主体, 其振子强度约占整个A带吸收的79%.由弥散轨道参与的n→Ryd 和π_H→Ryd 跃迁在B带跃迁中扮演重要角色, 其振子强度约占B带吸收的62%,而在A带吸收中占主导的π_H→π_L^*跃迁的振子强度在B带吸收中仅占33%. 嘌呤环变形伸缩+C8H/N9H面内弯曲振动ν₂₃和五元环变形伸缩+C8H弯曲振动ν₁₃的基频、泛频和合频占据了A带共振拉曼光谱强度的绝大部分, 说明¹π_Hπ_L^*激发态结构动力学主要沿嘌呤环的变形伸缩振动, N9H/C8H/C2H弯曲振动等反应坐标展开, 而ν₁₀, ν₂₉, ν₂₁, ν₂₆和ν₄₀的基频、泛频和合频占据了B带共振拉曼光谱强度的主体部分, 它们决定了B带激发态的结构动力学. A带共振拉曼光谱中ν₂₆和ν₁₂被认为与1nπ*/1ππ*势能面锥型交叉有关. B带共振拉曼光谱中ν₂₁的激活与¹ππ^*/¹πσ_N9H^*势能面锥型交叉相关.     

Analysis of the putative Cr-Cr quintuple bond in Ar'CrCrAr' (Ar' = C6H3-2,6(C6H3-2,6-Pr(i)2)2 based on the combined natural orbitals for chemical valence and extended transition state method

The nature of the putative Cr-Cr quintuple bond in Ar'CrCrAr' (Ar' = C(6)H(3)-2,6(C(6)H(3)-2,6-Pr(i)(2))(2)) is investigated with the help of a newly developed energy and density decomposition scheme. The new approach combines the extended transition state (ETS) energy decomposition method with the natural orbitals for chemical valence (NOCV) density decomposition scheme within the same theoretical framework. The results show that in addition to the five bonding components (σ(2)π(2)π'(2)δ(2)δ'(2)) of the Cr-Cr bond, the quintuple bond is augmented by secondary Cr-C interactions involving the Cr-ipso-carbon of the flanking aryl rings. The presence of isopropyl groups (Pr(i)) is further shown to stabilize Ar'CrCrAr' by 20 kcal/mol compared to the two Ar'Cr monomers through stabilizing van der Waals dispersion interactions.     

IB 族金属-乙烯配合物[N{(Me)C(Ph)N}2]M-C2H4 (M=Cu,Ag, Au)的电子结构

采用从头算Hartree-Fock(HF),M??ller-Plesset微扰(MP2),二级近似耦合簇(CC2)和密度泛函理论(DFT)方法,对IB族金属-乙烯配合物LM-C2H4(L=[N{(Me)C(Ph)N}2];M=Cu,Ag,Au)的几何结构、电子结构以及LM与C2H4之间的结合能进行了理论研究.MP2、CC2和密度泛函方法对C2H4配位前后C=C键长的变化情况都给出了正确的描述.电子结构分析显示LM与C2H4之间主要以C2H4→LM"σ-给予"和LM→C2H4"π-反馈"方式协同成键,这种成键方式使C2H4配体π轨道上的电子密度下降,π*轨道上的电子密度增加,并使得C=C键长增加、键能下降,从而达到活化C=C键的目的.自然电荷布居和能量分解分析显示LM-C2H4中的"σ-给予"作用弱于"π-反馈"作用,若使用"σ-给予"作用强于"π-反馈"作用的M+-C2H4体系作为LM-C2H4的简化模型进行理论研究是不合适的.LM-C2H4中金属原子M的改变对C=C键长、C2H4电荷布居以及LM与C2H4之间的结合能等性质影响显著.LAu与LCu、LAg相比其接受和反馈电子的能力最强,使C2H4配体π轨道电子密度减少的程度和π*轨道电子密度增加的程度也最大,因此LAu对C2H4中C=C键的活化效果最好.螯合配体取代基供、吸电能力的改变对上述性质的影响则非常有限.     

Supramolecular Self-assembly Behaviors of Asymmetric Diblock Copolymer Blends with Hydrogen Bonding Interactions between Shorter Blocks Modelled by Yukawa Potentials

We employed the extended self-consistent field theory to investigate the supramolecular self-assembly behaviors of asymmetric diblock copolymer blends (AB/B'C) with hydrogen bonding interactions between shorter B and B'blocks.The hydrogen bonding interactions are described by Yukawa potentials,where the hydrogen bonding donors and acceptors were modelled as two blocks smeared with opposite screened charges.The hierarchical microstructures with parallelly packed lamellae-in-lamellae (Lam) and 4.8.8 Archimedean tilting pattern(4.8.8) were observed at lower and higher hydrogen bonding density (θ),respectively.The hierarchy of Lam and 4.8.8 were demonstrated by the one-and two-dimensional density profiles and the underlying order of the large-length-scale and small-length-scale microstructures were also clarified.It was found that the 4.8.8 is favorable to the stronger hydrogen bonding density or interactions.As θ increases,the microphase transition from Lam to 4.8.8 occurs at θ=0.34,which is mainly attributed to the optimization of the electrostatic energy and conformational entropy with sacrificing the interfacial energy.This work can provide a new strategy to understand the supramolecular self-assembly as well as the mechanism behind the formation of complex hierarchical microstructures.     

Stacked but not Stuck: Unveiling the Role of π→π* Interactions with the Help of the Benzofuran–Formaldehyde Complex

The 1:1 benzofuran–formaldehyde complex has been chosen as model system for analyzing π→π* interactions in supramolecular organizations involving heteroaromatic rings and carbonyl groups. A joint “rotational spectroscopy–quantum chemistry” strategy unveiled the dominant role of π→π* interactions in tuning the intermolecular interactions of such adduct. The exploration of the intermolecular potential energy surface led to the identification of 14 low-energy minima, with 4 stacked isomers being more stable than those linked by hydrogen bond or lone-pair→π interactions. All energy minima are separated by loose transition states, thus suggesting an effective relaxation to the global minimum under the experimental conditions. This expectation has been confirmed by the experimental detection of only one species, which was unambiguously assigned owing to the computation of accurate spectroscopic parameters and the characterization of 11 isotopologues. The large number of isotopic species opened the way to the determination of the first semi-experimental equilibrium structure for a molecular complex of such a dimension.