二氧化碳水合物小晶穴和大晶穴的密度泛函研究

本文通过B3LYP方法,在6-31G(d,p)水平下对结构Ⅰ型二氧化碳水合物的十二面体小晶穴和十四面体大晶穴的结构进行优化,并计算了其振动频率.13C-NMR化学屏蔽常数及电子密度.结果表明,水合物晶穴的氢键键能强于水分子二聚体和冰晶格中的氢键键能.由此可以看出结构Ⅰ型二氧化碳水合物的晶穴是由氢键组成的稳定结构.通过CO2分子与大、小晶穴的范德华能比较,发现C02分子在大晶穴中更稳定.所计算出的C=O键的不对称伸缩振动频率和13C-NMR化学屏蔽常数与文献中的实验值基本一致.通过分析CO2与晶穴的电子密度,其结果与氢键键能计算结果一致,计算结果还表明,CO2在大晶穴中的稳定性较在小晶穴中的稳定性强.     

环状寡聚D-乳酸的理论研究

在CAM-B3LYP/6-311+G*水平,研究了气相中环状寡聚D-乳酸的几何结构、能量学特征和谱学性质,并进行了概念密度泛函分析。环状结构中存在3种不同类型的分子内氢键。PDLA6结构中的甲基基本在环的同一侧,偶极矩大;PDLA5的甲基在两侧均衡分布,偶极矩较小。PDLA4是能量学上最有利的结构。当聚合度n为偶数时,随着n的增大PDLAn的??G呈阶梯状增加,?ε呈阶梯状减小;当n为奇数时,也存在相同的现象。环状寡聚D-乳酸结构中C=O、COO―H和O―H键的伸缩振动频率与实验值相比,发生蓝移。PDLA6的电负性和亲电指数均为最大,表现出的酸性最弱。     

3个[AlB5O7（OH）6]2-簇的电子结构和红外光谱的DFT研究

采用密度泛函(DFT)方法,在B3LYP/6-311g*基组下,对3个[AlB5O7(OH)6]2-簇(I, II, III)的电子结构、稳定性和红外光谱进行了理论研究。结果显示3个簇中优化的键长和键角值与wiberg键级有关。[AlB5O7(OH)6]2-(I)的带宽最大,能量最低,稳定性最高。红外光谱研究显示BO3、BO4和AlO4基团振动频率的大小为BO3>BO4>AlO4,且BO3基团的振动强度也最大。此外,研究也显示非端基B-O键的振动频率较端基B-O键的振动频率大。     

密度泛函论1-乙基-3-甲基咪唑四氟硼酸盐离子液的结构和性质

离子液以其独特的性质广受关注,被誉为"绿色设计者溶剂",人们对其潜在的利用价值做了大量的研究.本文采用半经验PM3法和密度泛函(DFT)方法相结合,计算研究1-乙基-3-甲基咪唑四氟硼酸盐([EMIM][BF4])离子液的分子结构及其氢键作用.经PM3法预优化和在B3LYP/6-31G(d)水平上再优化得到离子对的最稳定结构,通过自然键轨道(NBO)分析阴阳离子间的电荷分布,经振动频率和强度分析得理论红外谱图.结果发现:[EMIM][BF4]离子液阴阳离子间有电荷转移,咪唑环上靠近阴离子的C-H键伸缩振动频率发生红移,且振动强度加强,阴阳离子间存在着弱氢键的作用.     

三呋咱并氧(氮)杂环庚三烯的密度泛函理论研究

以4种新型三呋咱并氧(氮)杂环庚三烯分子为研究对象,采用密度泛函理论B3LYP/6-31G(d,p)方法优化了其结构,得到了最优几何构型,并在振动分析的基础上求得体系的振动频率和IR谱,通过键级和键离解能(BDE)计算考察了4种分子的稳定性,在密度和生成焓计算基础上利用Kamlet-Jacobs公式预估了其性能。结果表明:当呋咱环上的N原子被氧化形成N→O配位键,与该N原子相连的O—N键和C—N键键长增大,与该N原子相间的N—O键和C—C键键长减小,除了氧化呋咱环上N—O—N键角显著减小外,其余键角无明显变化,二面角的变化幅度非常小,整个分子近乎在同一平面上;4个化合物的热稳定性均较好,但当呋咱环被氧化成为氧化呋咱环后,化合物的热稳定性显著降低,其热稳定性顺序为TFZN-1TFZO-1TFZN-2≈TFZO-2;呋咱环被氧化后能够大幅度提高炸药的爆轰性能,预估爆速在7600~8100 m/s范围,且与实测值吻合较好。     

3个[AlB5O7（OH）6]2-簇的电子结构和红外光谱的DFT研究（英文）

采用密度泛函（DFT）方法,在B3LYP/6-311g*基组下,对3个[AlB₅O₇（OH）₆]^2-簇（Ⅰ,Ⅱ,Ⅲ）的电子结构、稳定性和红外光谱进行了理论研究。结果显示3个簇中优化的键长和键角值与wiberg键级有关。[AlB₅O₇（OH）₆]^2-（Ⅰ）的带宽最大,能量最低,稳定性最高。红外光谱研究显示BO₃、BO₄和AlO₄基团振动频率的大小为BO₃>BO₄>AlO₄,且BO₃基团的振动强度也最大。此外,研究也显示非端基B-O键的振动频率较端基B-O键的振动频率大。     

直链酸与水相互作用的理论研究

采用量子化学方法中的密度泛函理论B3LYP方法,在B3LYP/6-311++G(d,p)基组水平上,对直链酸(甲酸至庚酸)与单分子水形成的体系进行结构优化和频率计算,从分子水平上研究了体系的相关的结构参数、电荷分布以及结合能,运用AIM理论分析了体系的电了密度拓扑。结果表明:直链酸与水形成两个氢键,其中羧基中氢原子作为质子供体的氢键1的键能强于水的氢作为质子供体的氢键2的键能。氢键1对体系的结合能影响起主导作用。稳定构型为六元环构型。直链酸与水结合能不随碳链增长呈明显变化,在(38.7-39.7)kJ/mol之间。     

环硼氮烷与IIIB族金属形成复合物的结构及性质研究

采用密度泛函理论的B_3LYP和PBE1PBE方法,研究了环硼氮烷B_3N_3H_6与IIIB金属Sc、Y、La形成的复合物B_3N_3H_6M和(B_3N_3H_6)_2M(M=Sc、Y、La)的结构和性质。结果表明:具有半夹心结构的复合物B_3N_3H_6M(M=Sc、Y、La)为最稳定结构,(B_3N_3H_6)2M(M=S c、Y、La)复合物的最稳定结构为重叠型。结合能的计算结果表明,结合能均为负值,说明形成复合物的过程为放热过程。复合物的HOMO值依次增大,而能隙依次减小,表明稳定性依次减弱。在红外吸收光谱中,相对于B_3N_3H_6,复合物B_3N_3H_6M和(B_3N_3H_6)_2M(M=Sc、Y、La)中B-N、B-H和N-H键的伸缩振动频率都向低波数方向移动,即发生了红移。     

碳原子簇Cn(n=2-20)的结构优化及构型转换

将并行快速退火演化算法结合Brenner势能函数用于小碳原子簇Cn(n=2—20)的结构优化，得到了最稳定构型：C2-C4为线型结构；C5-C17，为单环；C18和C19为类富勒烯的笼状结构；C30为最小的富勒烯。在Brenner势中使用了关于键级的修正项Fij以考虑成键轨道的非正常重叠和非、局域效应，研究了Fij项对碳原子簇键级以及结构转变产生的影响和原因，结果表明该修正项可以降低多环碳原子簇的键级，使得原子簇C18和C20的最稳定结构发生从多环到笼状的转变。     

C80-C90富勒烯结构与稳定性的理论研究

本文结合分子力学、半经验PM3和密度泛函(DFT)B3LYP方法对C80-C90的非分离五元环异构体和所有分离五元环异构体进行了理论研究。计算得到的B3LYP／6-31G的最低能量结构与文献报道一致。而且,对于C80-C90,并不存在一个特别稳定的非分离五元环异构体,分离五元环规则仍适用于富勒烯C80-C90。     

BC2nB(n=1-5)的理论研究

用Gaussian94程序包,在B3LYP／6-311 G**上对线型碳链BC2nB(n=1-5)进行了研究。它们属于D∞h点群．具有特殊的结构,用电子布居分析和振动模式分析来研究这种特殊结构。振动分析表明,属于平面弯曲和面内摇摆的振动模式是简并的,并且属于g对称性的所有面内弯曲和对称伸缩模式都没有或仅有很弱的IR活性。非对称伸缩模式(∑(?))总是有特别高的IR活性。     

Structural, electronic, and magnetic properties of two isomers of C40 O10 with cage-like structure

Bonding, vibrational and magnetic properties of two isomers of cage-like molecule C40 O10 are studied by using hybrid DFT calculations at the B3LYP/6-31G* level of theory. Infrared- and Raman-active vibrational frequencies of two isomers of C40 O10 are assigned. Three 13C and one 17O nuclear magnetic resonance (NMR) spectral signals of each isomer are characterized. Heat of formation of each isomer is estimated. Compared the stability of the two isomers of C40 O10 with that of C60, only from the thermodynamic points of view, they are more stable than C60. Thus, we believe that they have sufficient stability to allow their experimental preparation. We proposed their synthesized route in this paper.     

用密度泛函理论研究非诺贝特的构象和振动光谱

采用密度泛函B3LYP方法在6-31G*水平上对降血酯药物非诺贝特的构象和振动光谱进行了研究,得到了非诺贝特分子的平衡结构参数,并同文献中报道的非诺贝特晶体结构进行了比较,计算了目标分子在平衡构型下的振动基频和强度,计算结果表明,能量最低的构象其构型参数与实验值吻合最好,键长和键角分别只相差0.0123 A和1.52°,计算得到的红外图谱与实验结果相吻合,根据DFT计算的振动模式和IR光谱强度值对目标分子的实验振动基频进行了合理的指认和解释.     

4,6-双-(5-氨基-3-硝基-1,2,4-三唑-1-基)-5-硝基嘧啶(DANTNP)性能的量子化学研究

用B3LYP法,在6-31G(d,p)基组水平上计算4,6-双-(5-氨基-3-硝基-1,2,4-三唑-1-基)-5-硝基嘧啶(DANTNP)的性能,得其稳定的几何构型和键级;在振动分析的基础上求得体系的振动频率、IR谱及不同温度的热力学性质及温度对热力学性能影响的关系式。用UHF-PM3法探讨其热解机理,求得热解反应时的过渡态和活化能,发现热解始于N-H键断裂时。     

Post Hartree-Fock and density functional theory studies on structure and conformational stability of nitrosoethylene and substituted compounds of nitrosoethylene

Post Hartree-Fock and density functional theory (DFT) methods were used to study the different conformers of nitrosoethylene H-CH=CH-NO, and substituted compounds of the nitrosoethylene R-CH=CH-NO (R = Cl, NH2, N(CH3)2, OH, OCH3). The molecules were optimized at MP2/6-31G* level of theory of ab initio and B3LYP/6-31G* and B3PW91/6-31G* levels of theory of DFT. Special emphasis has been given to the effect of substitution of pi-electron donor groups NH2, N(CH3)2, OH, and OCH3, which play a major role in modifying the geometrical parameters of -N=O group by the electronic transmission effects through the central group -CH=CH-. The ability of DFT methods to predict the bond length adjacent to the atoms having lone pair electrons has been discussed. The conformational stabilities have been studied using the relative energies and DFT parameters such as chemical hardness and chemical potential. The role of intra-molecular hydrogen bond on the equilibrium structure has been discussed. The vibrational spectra for the different conformers of the nitrosoethylene and substituted compounds have been generated using the MP2/6-31G* level of theory.     

Endohedral complex of fullerene C60 with tetrahedrane, C4H4@C60

B3LYP/6-31G(d) hybrid HF/DFT calculations were carried out to determine the structural and electronic properties of the endohedral complex of C60 with tetrahedrane C4H4. It was demonstrated that C4H4 was seated in the center of the C60 cage and existed in a molecular form inside the fullerene. The formation of this complex was endothermic with inclusion energy of 141.05 kcal/mol. C4H4 endohedral doping slightly perturbed the molecular orbitals of C60. The calculated HOMO-LUMO gaps, the electron affinity(EA) and the ionizational potential (IP) indicated that C4H4@C60 seemed to be more kinetically reactive than C60. The IR active modes and harmonic vibrational frequencies of C4H4@C60 were also discussed.     

Theoretical investigation on carbon-centered tri-s-tetrazine and its 10 derivatives

A novel species, carbon-centered tri-s-tetrazine (C(4)N(9)H(3)), and its 10 derivatives (C(4)N(9)R(3), where R=OH, F, CN, N(3), NH(2), NO(2), N=NH, N(2)H(3), C triple bond CH, and CH=CH(2)) have been studied computationally. Density functional theory (DFT) has been used to study the geometries, electronic structure, harmonic vibrational frequencies, ionization energies of the 11 compounds at the restricted (for neutrals) and the unrestricted (for cations) B3LYP/cc-pVDZ level of theory. Atoms in molecule (AIM) and natural bond orbital (NBO) analyses have been used to obtain the bonding properties. Valence bond (VB) theory is applied to explain the unusual pyramidal structure around the carbon-center and electron arrangements of orbitals. We found: (1) All the species possess novel bonding features and geometrical structures. The atoms on the periphery of each species are sp(2) hybridized. Each of these atoms offers an orbital to form an extensive conjugation system (12)pi(15) (a pi system consisting of 12 centers and 15 electrons). The central carbon atom C13 is sp(3) hybridized, which makes the non-planar molecule shape like a straw-hat. Atom C13 also participates in the conjugated pi system with its sp(3) hybridized orbital, thus forming an extensive (13)pi(16) conjugate pi system covering the whole C(4)N(9) framework. (2) The change of charge on C13 is the largest among all the atoms when the species is ionized and the atomic charges are redistributed. In other words, C13 is the attack center for electrophilic agents. Thus, the species is carbanion-like. (3) All the species have low ionization energies (IEs). The electron ionized mainly comes from C13. They may have wide applications in organic chemistry, in organometallic chemistry and in alkyl lithium chemistry once they are synthesized.     

二硝基吡唑并吡唑性能的量子化学研究

用B3LYP法,在6-31G(d,p)基组水平上计算二硝基吡唑并吡唑(DNPP)的性能,得其稳定的几何构型、分子轨道及键级;在振动分析的基础上求得体系的振动频率、IR谱及不同温度下的热力学性质,并得温度对热力学性能影响的关系式;用Monte-Carlo方法从理论上计算密度,运用Kamlet公式预测爆速。     

QM/MM and SCRF studies of the ionization state of 8-methylpterin substrate bound to dihydrofolate reductase: existence of a low-barrier hydrogen bond

Using combined semiempirical quantum mechanics and molecular mechanics (QM/MM) and ab initio self-consistent reaction field (SCRF) calculations, we determined that a low-barrier hydrogen bond (LBHB) is formed when the mechanism-based substrate 8-methylpterin binds to dihydrofolate reductase (DHFR). The substrate initially was assumed bound either in the ion-pair form corresponding to N3-protonated substrate hydrogen (H) bonded to the unprotonated (carboxylate) of the conserved Glu30 residue in the active site, or in the neutral-pair form corresponding to unprotonated substrate H bonded to the neutral (carboxylic acid) from of Glu30. The free energy of interaction of these H-bonded systems with the protein/solvent surroundings was computed using a coordinate-coupled free energy perturbation (FEP) method implemented within the molecular dynamics (MD) simulation scheme and using a semiempirical (PM3) QM/MM force field. The free energy obtained from the QM/MM force-field simulations corresponds most closely with the corresponding free energy component obtained from HF/6-31G* SCRF calculations using a value of 2 for the dielectric constant (epsilon) for the solvated protein. Calculations were performed at levels ranging from HF/6-31G to MP2/6-31G* to B3LYP/6-31 + G**, with varying dielectric constants. The energy-minimized path for motion of the proton in the H bond along a one-dimensional reaction coordinate was calculated at HF/6-31G, HF/6-31G* (epsilon = 1) and B3LYP/6-31G* (epsilon = 2) levels. These calculations identified a second neutral-pair complex, involving the 2-amino group of substrate, which also interacts with Glu30, which is lower in energy than the ion-pair form. A harmonic vibrational analysis shows that the first vibrational state appears to lie near or above the TS connecting potential energy minima corresponding to the two neutral-pair configurations, thus indicating an LBHB. Consequently, the H-bonded system will have a significant probability of being found in the ion-pair form, in agreement with experimental spectral studies indicating an enzyme-bound cation and suggesting that the LBHB would activate substrate towards hydride-ion transfer from NADPH.