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为计算相互作用较弱的分子碎片之间的耦合能,Harris从密度泛函理论出发,提出了一种简化方法,即冻结密度近似(FDA)方法.对该方法在描述分子间氢键作用的合理性进行了验证.对水分子间的HO┉H氢键、甲酰胺与水分子间的NH┉O氢键、二氟甲烷和水分子间的OH┉F氢键,以及DNA中的碱基(AT,GC)之间的N—H┉O,N—H┉N等类型的氢键的计算表明:若电子交换关联采用非定域自旋密度近似,FDA的计算结果同其他abinitio方法的计算结果以及实验结果都符合得很好.FDA在计算过程中既不需要求解泊松方程,也不需要进行反复的自洽迭代,所以运算速度较快,在研究生物大分子体系中的氢键相互作用方面具有一定的使用价值
关键词:
冻结密度近似
氢键
密度泛函 相似文献
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利用第一性原理计算了胺和二芳基碳正离子的亲核反应的速率常数. 研究不同的溶剂化模型(PCM、CPCM和COSMORS)、不同类型的原子半径(UA0、UAKS、UAHF、Bondi和UFF)、以及一些单点能计算方法(B3LYP、B3P86、B3PW91、BHANDH、BMKPBEPBE、M06、MP2和ONIOM)在计算这类速率常数时的表现.通过比较速率常数的实验值和计算值,发现ONIOM(CCSD(T)/6-311++G(2df,2p):B3LYP/6-311++G(2df,2p))//B3LYP/6-31G(d)/PCM/UFF方法表现最好. 该方法随后被用于计算更多的胺和二芳基碳正离子的亲核反应的速率常数. 65个反应的速率常数的实验值和计算值之间表现出了相当好的相关性,这表明该方法适用于计算胺二芳基碳正离子的亲核反应的速率常数. 相似文献
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提出了重组能的量子化学算法 ,在用CISD/6 31G基组水平上 ,得到苯硝化反应中反应物及过渡态的结构 .并计算了各自交换电子转移反应以及交叉电子转移反应的重组能 ,同实验重组能进行了比较 .计算用了Gaus sian 94程序 .从重组能的角度分析了苯硝化反应 .结果表明 ,对于NO2 + +NO2 →NO2 +NO2 + 的自交换电子转移反应 ,重组能较大 ,结论为 :在芳烃硝化反应中 ,存在以NO2 + 为氧化剂的电子转移步骤的可能性很小 ,而从动力学的角度上 ,用NO+ 作反应的氧化剂更有可能 . 相似文献
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《物理学报》2016,(22)
利用扫描隧道显微镜研究水分子在吸附有氧原子的Cu(110)表面的吸附与分解过程.室温条件下,氧原子(O)在Cu(110)表面吸附并自组装形成规则的沿[001]方向的(2×1)Cu-O链状结构.将吸附有氧原子的Cu(110)样品置于77 K低温条件下观察水分子的吸附与分解,发现在低温下水分子通过氢键与Cu-O链中的氧原子键合而吸附于Cu-O链的顶部和周围,吸附于Cu-O链周围的水分子自组装形成规则的六边形网状结构.通过针尖隧穿电子激发,六边形网状结构中的水分子与氧原子发生化学反应,反应生成的羟基与未参与反应的水分子键合在裸露的Cu(110)表面形成蜂窝网状结构.研究结果表明,Cu(110)表面吸附的氧原子有助于水分子在金属表面的吸附和组装,同时可以催化金属表面水分子的分解反应,对水汽转换实验研究具有一定的指导意义. 相似文献
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利用四体模型计算了100和2MeV/amu裸碳单电离氦原子的全微分截面,其结果与实验数据和其它理论进行了比较.对于高能入射情况,在散射平面小动量转移和中间动量转移时现在的理论结果和实验符合的很好,然而在大动量转移时和在垂直平面有明显差异.对于低能入射情况,四体结果定性与实验结果一致,而且优于三体扭曲波(3DW-EIS)结果,表明四体效应在低能入射比在高能入射时明显. 相似文献
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《原子核物理评论》2020,(2)
基于改进的量子分子动力学(ImQMD)模型,模拟了~(136)Xe+~(208)Pb在质心系入射能量为E_(c.m.)=617MeV的多核子转移反应。为了研究这个特殊的反应体系,将不同核子数转移前后形成的类弹与类靶对应的Q值的指数概率分布引入模型中考虑Q值效应,并将计算结果与实验探测的总动能损失分布和质量分布进行了比较。我们发现考虑Q值效应后的计算结果更好地再现了实验数据。在少于10个核子的转移过程中,核子的转移明显受到了Q值效应的驱动。在更多的核子转移过程中,Q值效应明显压低了反应产物的生成截面。这是因为大量的核子转移主要发生在小碰撞参数,对应的复合体系的寿命由于Q值效应明显减小。在ImQMD与ImQMD+Q的计算结果比较中,我们还发现,Q值效应明显增加了比208Pb更丰中子的中子数为126的初级碎块生成截面。 相似文献
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DFT at B3LYP/6-31G (d,p) level calculation results for the amine-catalysed isomerization of dimethyl maleate revealed that the mechanism proceeds via four steps: (1) a concerted proton transfer from one amine molecule to another which subsequently enhances the addition of the adduct thus formed to the C–C double bond to yield INT1. (2) Abstraction of a proton from the β-carbon of INT1 by a second amine molecule to give intermediate INT2. (3) Rotation about the C–C single bond followed by proton abstraction by an amine molecule to yield unstable INT3, and (4) an elimination of an amine molecule to yield the trans isomer, dimethyl fumarate. Furthermore, it was found that step 1 is the rate limiting step. However, the activation energy difference between steps 1 and 2 was significantly low and its value depends on the amine catalyst used. The activation energy was found to be lower in water when compared to that calculated in the gas phase. In addition, linear correlation was found between the amine-catalysed isomerization experimental rate and the pKa of the amine catalyst on one hand and the enthalpic and free activation energies on the other hand. The calculations also confirmed that the reaction is first order in dimethyl maleate, second order in the amine catalyst and overall third order. This study disproves three of the four different intermediates that were previously suggested to explain the amine catalysed isomerization of dialkyl maleates. The study verifies the intermediate suggested by Rappoport. 相似文献
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用密度泛函理论在B3LYP/6-31G(d,p)计算水平下研究了次氯酸钠氧化邻硝基苯胺生成苯并氧化呋咱的环氧化反应.考虑溶剂化效应对反应的影响,使用极化连续反应场模型进行几何优化.计算了该反应的两种可能反应通道,它们都是分步反应,反应通道A经历氧化、移氢、脱水和环化四步反应,在反应通道B中,氢氧化钠的OH-首先进攻邻硝基苯胺的胺基H原子,生成邻硝基苯亚胺负离子.计算结果表明,在反应通道A是可行的反应通道,1个水分子辅助进行分子内脱水反应是速控步骤. 相似文献
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The proton MAS NMR spectra in MCM-41 at low hydration levels (less than hydration amounting to one water molecule per surface hydroxyl group) show complex proton resonance peak structures, with hydroxyl proton resonances seen in dry MCM-41 disappearing as water is introduced into the pores and new peaks appearing, representing water and hydrated silanol groups. Surface hydroxyl group–water molecule chemical exchange and chemical shift averaging brought about by a water molecule visiting different surface hydrogen bonding sites have been proposed as possible causes for the observed spectral changes. In this report a simple model based on chemical shift averaging, due to the making and breaking of hydrogen bonds as water molecules move on the MCM-41 surface, is shown to fully reproduce the NMR spectra, both as a function of hydration and temperature. Surface proton–water proton chemical exchange is not required in this model at low hydration levels. 相似文献
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Optimization of the irradiation power in chemical exchange dependent saturation transfer experiments
Sun PZ van Zijl PC Zhou J 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,175(2):193-200
In chemical exchange dependent saturation transfer imaging experiments, exchangeable solute protons are saturated and the transfer of saturation to water is subsequently detected. When the applied irradiation power is comparable to the resonance frequency difference between the water protons and saturated solute protons, the proton transfer (PT) efficiency is reduced due to concomitant direct saturation effects. In this study, the PT process is modeled using a two-pool system. An empirical general proton transfer ratio (PTR) equation for arbitrary RF irradiation power is derived, and its optimal power to maximize the PTR is analyzed. The results are confirmed experimentally on 4.7 T using a poly-L-lysine solution. The theory provides a useful tool for optimizing the irradiation power of the PT sequences in the presence of direct saturation effects. 相似文献
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Hong-Bin Zhan 《中国物理 B》2022,31(3):38201-038201
The fluorescence mechanism of HBT-HBZ is investigated in this work. A fluorescent probe is used to detect HClO content in living cells and tap water, and its structure after oxidation by HClO (HBT-ClO) is discussed based on the density functional theory (DFT) and time-dependent density functional theory (TDDFT). At the same time, the influence of the probe conformation and the proton transfer site within the excited state molecule on the fluorescence mechanism are revealed. Combined with infrared vibrational spectra and atoms-in-molecules theory, the strength of intramolecular hydrogen bonds in HBT-HBZ and HBT-ClO and their isomers are demonstrated qualitatively. The relationship between the strength of intramolecular hydrogen bonds and dipole moments is discussed. The potential energy curves demonstrate the feasibility of intramolecular proton transfer. The weak fluorescence phenomenon of HBT-HBZ in solution is quantitatively explained by analyzing the frontier molecular orbital and hole electron caused by charge separation. Moreover, when strong cyan fluorescence occurs in solution, the corresponding molecular structure should be HBT-ClO(T). The influence of the intramolecular hydrogen bond formation site on the molecule as a whole is also investigated by electrostatic potential analysis. 相似文献
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7-羟基喹啉(7-HQ)是一种具有激发态质子转移(ESPT)效应的有机分子。它溶于乙醇溶剂中,在紫外光的激励下,将发生ESPT反应,荧光光谱出现2个荧光带。7-HQ溶于二甲基亚砜(DMS)溶剂中,则不能发生ESPT反应,其荧光光谱只出现单一荧光带。但样品被强紫外光照射后,其荧光光谱也出现2个荧光带。文章首次报道了这一现象,并通过对7-HQ的乙醇、二甲基亚砜和二甲基甲酰胺溶液的吸收光谱和荧光光谱的研究,探讨产生这一现象的机理。认为7-HQ溶于DMS中被强紫外光照射后荧光光谱的变化是由于DMS被光解并生成水而使7-HQ发生ESPT反应的结果。 相似文献
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Brena B Nordlund D Odelius M Ogasawara H Nilsson A Pettersson LG 《Physical review letters》2004,93(14):148302
Using x-ray emission and photoemission spectroscopies to measure the occupied valence levels in a thin crystalline ice film, we resolve the ionization-induced dissociation of water in ice on a femtosecond time scale. Isotope substitution confirms proton transfer during the core-hole lifetime in spite of the nonresonant excitation. Through ab initio molecular dynamics on the core-ionized state, the dissociation and spectrum evolution are followed at femtosecond intervals. The theoretical simulations confirm the experimental analysis and allow for a detailed study of the dissociative reaction path. 相似文献
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In the light-driven proton pump bacteriorhodopsin, photoisomerization of the all-trans retinal chromophore triggers a photocycle whose net effect is the transfer of one proton from the cytoplasmic to the extracellular side of the membrane. The first proton transfer step, from the retinal Schiff base to Asp85, occurs between the L and M intermediate states. Details of the geometry of the retinal binding region are important for the pathway followed by the proton. Here we report some preliminary results on combined Quantum Mechanical/Molecular Mechanical reaction path calculations for retinal deprotonation and discuss the hydrogen-bonding pattern in the active site. 相似文献
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Optically detected electron paramagnetic resonance technique has been applied to study the stability of sterically hindered
amine radical cations with respect to the ion–molecule proton transfer reaction in liquid squalane solutions. The reaction
has proved very sensitive to the steric effect of bulky tertiary substituents at the nitrogen atom. It has been established
that steric hindrance is able to efficiently block the N–H proton transfer reaction, while the H-bonding may stabilize the
distonic intermediate complex of aminyl radical and cation of ammonium type. 相似文献