光场算符n次幂叠加激发混沌场的量子特性

构造了光场算符n次幂叠加激发混沌场,采用数值计算方法研究了该量子态的压缩效应、反聚束效应和统计性质,讨论了混沌场平均光子数、算符叠加系数及其幂次n对量子特性的影响.研究结果表明:光场算符n次幂叠加激发混沌场不呈现压缩效应,但呈现出反聚束效应和亚泊松分布性质,并且随平均光子数增大,它的反聚束效应和亚泊松分布性质减弱;随着算符组合部分中产生算符的比重增大,光场反聚束效应和亚泊松分布性质增强;随着算符幂次增大,亚泊松分布性质加强.     

Glauber相干态的激发态及其非经典效应

构造了Glauber相干态的激发态,数值计算表明该激发态不仅显示反聚束效应,也呈现亚泊松分布.     

准SU(1,1)相干态的亚泊松分布特性

数值计算显示准SU(1,1)相干态呈亚泊松分布,这是没有经典对应的量子特性.     

叠加激发双模SU(2)相干态的量子统计特性

构造了叠加激发双模SU(2)相干态|ψ＞=Cm(| M,ξ;m＞+eiφ| M,ξ*;m＞),用数值方法研究它的量子统计特性.结果表明:叠加激发双模SU(2)相干态两场模的光子统计分布保持反关联特征,而且呈现奇特的光放大特性;b模光场的亚泊松分布得到比较大的加强,而a模光场的亚泊松分布特性则有轻微减弱;两场模的反聚束性均得到增强;随激发量子数m的增大,两场模间的反关联性减弱.     

Λ型和V型三能级原子与耦合腔相互作用系统中场的量子特性

研究了能级结构分别为Λ型三能级和V型三能级结构的两个原子和通过光纤耦合的由双模腔构成的复合系统中光场的压缩效应、二阶相干度和亚泊松分布等量子特性。利用数值计算方法讨论了光纤模与腔场间的耦合强度对量子特性的影响。研究结果表明:双模光场不呈现压缩效应,但呈现出反关联和亚泊松分布的量子特性;随着光纤模与腔场间耦合强度的增强,亚泊松分布减弱。     

HIV-1蛋白酶的质子化状态

将分子动力学模拟和分子力学-泊松/波耳兹曼方法相结合,研究在HIV蛋白酶和抑制剂ABT-538的复合物中的不同质子化位置.结果表明：不同的质子化状态对蛋白酶的温度因子、蛋白酶和抑制剂的结合自由能及氢键都有很大影响.用分子力学-泊松/波耳兹曼方法计算显示：在B链中,25号天冬氨酸OD1氧原子被质子化的结合自由能最强,计算得到的温度因子和实验值比较吻合.另外,由氢键分析看出：在此质子化状态中,药物和蛋白酶、药物和W301水分子、W301水分子和蛋白酶形成的氢键在整个动力学模拟过程中最稳定.     

双模最小关联混态的量子统计性质

研究了双模最小关联混态在不同参数情况下的量子统计性质.发现在一定的参数范围内双模最小关联混态的二阶相干性违反经典的Cauchy-Schwartz不等式,呈现非经典性相关;同时对双模最小关联混态的压缩特性、亚泊松分布等非经典性质进行了分析,通过数值计算得出,每模光子的压缩性及其亚泊松分布均与参数d的取值密切相关.     

压缩态光场在双光子吸收介质中的演化

采用生成函数方法,由光场密度算符主方程,求得光场压缩度s,二阶相干度g^(x)和光子统计分布的严格解析表达式,同时讨论它们随标度时间τ的演化。计算表明,在双光子吸收过程中,虽然压缩度s逐渐减弱,但相当长的时间内光场仍呈现压缩特性;该过程有利于呈现和增强光子反聚束效应和光子亚泊松分布特性;光子分布的振荡特征维持较短一段时间后很快消失。 关键词：     

扩散p-n结内建电场的数值分析

对高斯分布的p-n结,通过建立相关的一维泊松分布方程,分析边界和初始条件,应用数值计算方法在耗尽层近似和考虑自由载流子两种情况下模拟电场、电势的分布。进一步讨论温度变化对电场、电势分布的影响。     

压缩真空态的高阶非经典性质

通过高阶压缩效应,高阶反聚束效应和二阶亚泊松分布等统计性质,研究了压缩真空态的高阶非经典性质。采用数值计算方法,讨论了压缩参数对态的高阶非经典性质的影响。研究结果表明:压缩真空态呈现出高阶压缩效应和四阶反聚束效应,并且这些非经典性质均随压缩参数增大而增强。但它未呈现出一至三阶反聚束效应,也没有展示出一阶亚泊松分布和二阶亚泊松分布等特性。     

脉冲升温纳秒时间分辨中红外光谱研究氨基酸重水溶液的分子间氢键

应用变温傅立叶变换红外光谱和脉冲升温纳秒时间分辨红外差谱研究了组氨酸和甘氨酸的重水溶液的羧基负离子的振动．结果表明不仅氨基酸分子之间形成氢键，而且氨基酸分子和溶剂分子之间也形成氢键．当温度升高时，羧基负离子在1600?1610 cm?1 附近的反对称伸缩振动发生蓝移，说明高温使氢键减弱．温度从10℃突然升高到20℃，组氨酸的时间分辨瞬态光谱出现两个漂白峰，一个在1604 cm?1，指认为形成氨基酸分子间氢键的羧基负离子的峰；另一个在1612 cm?1，指认为氨基酸分子和溶剂分子形成氢键的羧基负离子的峰．前     

The hydrogen bond under pressure

The hydrogen bonds are quite pervasive in several classes of materials. Its parameters are known to show systematic variations with hydrogen bond length, and pressure variable is thus a natural way for studying hydrogen bonded substances. In this article, we review the unifying features as obtained through several experimental and theoretical investigations. Amongst other things, it is examined whether the observed pressure-induced variations in parameters of hydrogen bonds are consistent with the co-relations known on different chemical substances at normal pressure. In particular, the controversies on variations of O–H and H- - -O pairs with pressure and symmetrization of hydrogen bond have been resolved. The effects of close packing promoted by pressure such as formation of muli-centered hydrogen bonds and steric repulsions and the way the hydrogen bonds counter these in different ways are also examined.     

Dynamics and hydrogen bonding in liquid ethanol

Molecular dynamics simulations of liquid ethanol at three temperatures have been carried out. The hydrogen bonding states of ethanol molecules have been characterized by the number of hydrogen bonds in which the molecules participate. It is observed that the mean lifetimes of molecules in each hydrogen bonding state are markedly dependent on the temperature. Moreover, molecules with one hydrogen bond are more stable when they are donors than when they are acceptors. The dependence of the reorientational correlation functions on the hydrogen bonding state of molecules has been studied carefully. The decay of these functions is slower for molecules with higher numbers of hydrogen bonds and also becomes slower as temperature decreases. The relaxation for molecules with only one hydrogen bond is faster for those acting as proton donors than for those acting as proton acceptors. Finally, the results obtained by computer simulation are compared with those from recent measurements of the frequency-dependent dielectric permittivity of liquid ethanol.     

Structural studies of liquid alcohols by neutron diffraction

Neutron diffraction measurements have been made on methyl alcohol at room temperature for an incident wavelength of 0·94 Å. Cross sections have been obtained for CD₃OD, CD₃OH, and mixtures of these compounds. These data are subtracted to obtain the separated structure factors for intermolecular H₀H₀, the hydroxyl components, and the non-hydroxyl components. The Fourier transformations of the structure factors show components of both intra- and intermolecular distribution functions. Width parameters obtained from model fits are too large for thermal vibrations and are interpreted as geometrical broadening due to the stretching of bonds, variations in bond angles, and rotation of the methyl group. Differences in the real space distribution function between hydrogen and deuterium are noted.     

无序碳单层的电子结构及氢原子吸附的第一性原理

本研究运用第一性原理计算方法,系统地研究了无序碳单层材料不同位点的电子结构及其析氢性能.计算结果显示无序结构中的C-C键相比于石墨烯中的C-C键在26.7%的范围内有不同程度的拉伸或压缩,使得C原子电荷在-0.17～+0.16个电子范围内变化,导致部分C原子电子局域化.电子的局域化增强了C原子的化学活性,从而表现出了较强的吸附性能.我们发现H原子与C原子的键合及析氢性能与C原子间的键角相关.对于三配位的碳原子,其中三个价电子通过sp~2杂化轨道与最邻近的碳原子结合形成较强的共价键,而余下的一个p_z轨道电子可以与H原子在垂直于原子层的方向形成较弱的化学键.无序结构可以打破三个sp~2杂化轨道的对称性,进而影响p_z轨道与氢的成键.本研究在一定程度上揭示了单层无序碳材料结构-性能的构效关系,为实验上设计特定性能的无序碳功能材料提供理论指导.     

用低温光谱方法揭示氢键的结构特征

本文提出了一种利用红外光谱方法揭示晶态物质中分子的氢键结构的新方法。用ＫＢｒ压片和氟油研磨法制备于红光谱测量的样品。测得的光谱有时基本相同,有时同明显的差别。对此现象一直没有一个十分满意的解释。我们用低温红外光谱法证明压力诱导晶格中氢键网络的微细变化是造成不同产法测得的光谱不同的原因。具有平面氢键结构的晶体不能有效地的御加于样品上的应力,易一城较低的外力作用下发生结构畸变,因此,用ＫＢｒ压片和氟油     

Calculation of electronic spectra for intermolecular complexes of 3-aminophthalimide by a modified Hückel molecular orbital method

Calculation of the spectra of intermolecular complexes of 3-aminophthalimide is used as an example to show that when hydrogen bonds are present, the resonance integrals for the proton donor and acceptor atoms are different from zero. Theoretical analysis of strained 3-aminophthalimide complexes allowed us to establish the determining role of hydrogen bonds in their formation. Using an intramolecular peptide hydrogen bond as an example, we studied the effect of the solvent on its parameters. In particular, we showed that hydrogen bond formation with a proton-acceptor group of the chelate ring leads to a decrease in the resonance integral, and consequently a decrease in the enthalpy of formation of the intramolecular hydrogen bond, to a significantly greater degree than formation of a hydrogen bond at a proton-donor group. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 735–740, November–December, 2006.     

Effects of concentrated NaCl and KCl solutions on the behaviour of aqueous peptide bond environment: single-particle dynamics and H-bond structural relaxation

The effects of salt concentrations on the structure, dynamics and hydrogen bond structural relaxation properties of ～1.10 M aqueous N-methylacetamide (NMA) solution at 308 K are studied by classical molecular dynamics simulations. We have considered the concentration range of salts solution from 0.222 to 3.756 M to investigate the behaviour of aqueous environment of peptide bonds in the presence of concentrated NaCl and KCl solution. It is found that the addition of salt solution facilitates the structural breaking of aqueous NMA hydrogen bonds, as a result the number of hydrogen bonds per NMA molecule and their stability decreases. The water and NMA molecule shows slower translational and rotational dynamics with increasing salt concentrations due to additional ion atmospheric friction. Our result shows that the cation–O_NMA radial distribution function decreases whereas the Cl^?─H_NMA radial distribution function increases with ion concentration. On the other hand, the cation–O_water and Cl^?─H_water radial distribution function shows very negligible change with respect to ion concentration. We have also calculated NMA–water and water–water hydrogen bond structural relaxation times. It is observed that the hydrogen bond structural relaxation of O_NMA─H_water is comparatively slower than the H_NMA─O_water hydrogen bond, which can be attributed to higher number and greater stability of the former hydrogen bond than the latter. The change of the dynamical quantities observed here is more prominent in addition of NaCl rather than the KCl solution.     

Classical and path-integral molecular-dynamics study on liquid water and ice melting using non-empirical TTM2.1-F model

The TTMF2.1-F model is a non-empirical intermolecular water potential parametrised from ab-initio calculations of the water dimer with a complete basis set limit including dispersion correction from second-order Moller-Plesset perturbation theory. In this work, using two-phase ice-water NVT molecular-dynamics (MD) simulations, we found the ice melting temperature using the TTM2.1-F potential is close to 273?K when the nuclear quantum effects (NQEs) were included using path-integral centroid MD. Detailed analysis of the radial distribution functions, angle distribution functions, and associated joint probability for both liquid water and the two-phase cases showed that the melting-point-temperature drop when using path-integral simulation is due to the weakening of hydrogen bonds vis-à-vis classically-propagated MD.     

碳纳米胶囊中水分子的分子动力学研究

采用分子动力学方法研究了不同温度下碳纳米胶囊中水分子及其氢键的聚集密度分布,讨论了水分子内部键角及其取向规律.计算结果表明,由于碳纳米胶囊的束缚作用,水分子主要聚集在与胶囊形状相似的三个薄层中,随着温度的升高,聚集密度峰均会展宽并向管壁移动.氢键的分布规律与水分子聚集密度类似并对其取向角分布有明显影响.与通常情况不同,在1000K高温时仍存在相当数量的氢键.在3100 K附近,碳纳米胶囊发生破裂,溢出少量水分子后自动愈合.