Sensitivity of model water structure to hydrogen bond included

Water empirical pair potentials, including the nonelectrostatic component of hydrogen bond (HB), are considered. The sensitivity of the radial distribution functions (RDF), calculated in computer experiment, to this contribution is analyzed. The model potentials, for which the positions and the heights of first and second peaks on the oxygen–oxygen radial distribution function coincide with the experimental ones, have been obtained.     

A model of phase transitions in double-well Morse potential: Application to hydrogen bond

A model of phase transitions in double-well Morse potential is developed. Application of this model to the hydrogen bond is based on ab initio electron density calculations, which proved that the predominant contribution to the hydrogen bond energy originates from the interaction of proton with the electron shells of hydrogen-bonded atoms. This model uses a double-well Morse potential for proton. Analytical expressions for the hydrogen bond energy and the frequency of O–H stretching vibrations were obtained. Experimental data on the dependence of O–H vibration frequency on the bond length were successfully fitted with model-predicted dependences in classical and quantum mechanics approaches. Unlike empirical exponential function often used previously for dependence of O–H vibration frequency on the hydrogen bond length (Libowitzky, Mon. Chem., 1999, vol.130, 1047), the dependence reported here is theoretically substantiated.     

Metastable molecular fluid hydrogen at high pressures

Warm dense hydrogen is studied in the region of fluid–fluid phase transition within the framework of the density functional theory. We report a procedure of obtaining metastable states and calculate the equation of state. Metastable states are diagnosed by pair correlation functions and values of conductivity. We obtain a strong overlapping through the density of metastable and equilibrium branches of pressure isotherms. This indicates the plasma nature of the phase transition.     

Melting of metallic hydrogen at high pressures

The Lindemann equation was used to calculate the melting of metallic hydrogen. It is shown that, after transition from the molecular dielectric phase to the atomic metallic phase, hydrogen becomes a quantum liquid because of the atomic zero-point vibrations. The phase diagram of hydrogen is unique in that the molecular phase is the only solid phase of hydrogen.     

Melting line of hydrogen at high pressures

The insulator to metal transition in solid hydrogen was predicted over 70 years ago but the demonstration of this transition remains a scientific challenge. In this regard, a peak in the temperature versus pressure melting line of hydrogen may be a possible precursor for metallization. However, previous measurements of the fusion curve of hydrogen have been limited in pressure and temperature by diffusion of hydrogen into the gasket or diamonds. To overcome this limitation we have used an innovative technique of pulsed laser heating of the sample and find a peak in the melting line at P=64.7+/-4 GPa and T=1055+/-20 K.     

激发态下甘氨酸与水分子间氢键性质研究

在生物体中氨基酸通常以水作为溶剂,是形成细胞的重要成分.在该环境下,分子间氢键的产生会对氨基酸分子与水分子的结构和性质产生影响.为了研究其在基态和激发态下的性质,本文利用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)对甘氨酸分子和H₂O分子在基态和激发态下的分子间氢键的静电势、键长、自然键轨道(NBO)电荷、分子中的原子理论(AIM)分析、Wiberg键级b、红外(IR)光谱、空穴-电子轨道和基态与激发态之间的电子转移进行了理论研究.结果表明：分子间氢键的形成会导致分子结构的改变和红外光谱振动频率的移动.在激发态下,分子间氢键有不同程度的增强或减弱.该计算结果为氢键的形成和激发态下分子间氢键的研究提供理论依据.     

The effect of hydrogen bond breaking defect on charge transport in a DNA molecular device

The charge transport in a DNA molecular device is theoretically investigated based on the Lattice Green Function method and Landauer-Büttiker theory. The effect of a hydrogen bond defect at different sites is investigated. A defect at the end of the DNA molecule reduces the current through the molecule, but a defect in the middle region of the molecule will have relatively slight effect on the current through the molecule. The effect of defect on the wave function distribution at the ends of the DNA molecule plays an important role in the defect mediated transport properties.     

Dipole polarizability of hydrogen atom at high pressures

Dipole polarizability of hydrogen atom at high pressures is investigated using the model of a trapped atom inside a spherical box with impenetrable surface. Both upper and lower bounds for the polarizability are obtained using accurate variational wavefunctions proposed recently. Buckingham polarizabilities calculated from the 1s state wavefunction are shown to be in good agreement with those calculated from the exact values of rⁿ for cage radii less than 2.5.     

On the electronic structures of some conductive one-dimensional metal-glyoximes at high pressures

Bis(dimethylglyoximato)Pt(II)(PtDMG)₂) and its related complexes exhibit a remarkable decrease in electrical resistance at high pressures. The least resistivity and the activation energy observed for Pt(DMG)₂ are 10^?1 Ω-cm and 5 × 10^?3 eV, respectively. These low values are tentatively attributed to the effect of hyperconjugation to methyl substituent on the electric polarizability in the ligand.     

MgB2 and AlB2 at high pressures

We have studied the effect of pressure on vibrational and electronic properties of MgB₂ and AlB₂ by ab initio calculations and Raman spectroscopy. The comparison between the calculations and the Raman data puts the common assignment of a broad spectral feature near 600 cm^?1 in MgB₂ to the E _2g phonon into question. At variance with MgB₂ the Raman spectra of AlB₂ exhibit a well-defined E _2g mode indicating that the anomalous Raman spectrum encountered in MgB₂ is not related to the metallicity of the samples nor is it intrinsic to crystals of the AlB₂ structure type. A theoretical estimate of the pressure dependence of T _c in MgB₂ shows that the experimentally observed decrease of T _c under pressure is predominantly due to phonon frequency shifts.     

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.     

Ion hydration and hydrogen bond structure in NaCl solutions at temperatures and pressures for carbon dioxide sequestration: the effects of solvated CO2 molecules

In the present study, we focus on the phase properties of CO₂–brine systems in geologic media. Molecular dynamics simulation methods were used to investigate the ion hydration and hydrogen bond structure in CO₂–brine and brine solutions at temperatures and pressures for CO₂ sequestration. By comparing the results of CO₂–brine solutions with those of brine solutions, the effects of solvated CO₂ were analysed and discussed.     

高温高压下稠密氢的离解与电离

应用自恰变分自由能模型描述了在化学平衡下,H2,H,H ,e构成地混合物在天体物理和高压实验中遇到情形下的各种相互作用及压力与温度效应引起地离解和电离现象.目前的模型预测了在压力电离区存在一热力学不稳定状态,当温度Tc=15.5 kK,压力Pc=58.3 GPa和密度ρc=0.3226 g/cm3时发生等离子体相变,此理论预测结果与各种模型计算结果进行了比较分析.     

Anomalous compressibility and metallization of deuterium and hydrogen at high pressures

The high compressibilities recorded in experiments on liquid-deuterium compression and the significant scatter of experimentally measured densities in the region of anomalous compressibilities are explained by the manifestations of an unusual dielectric-metal phase transition: from a dense molecular gas to a liquid-metal atomic gas. This transition has previously been described by us and called the dissociative phase transition (DPT). The dissociative equilibrium curves, the isotherms, the DPT binodal, and the Hugoniot adiabat have been calculated. The DPT has been shown to be a transition of a new, non-van der Waals type.     

The statistical theory of the condensed system equation of state at high pressures

Abstract

One of the main problems in the statistical physics of condensed systems is the problem of the adequate equation of state to describe the thermodynamical properties of the substance in the wide range of pressure values. Here it is being solved by means of thermodynamic perturbation theory and the integral equations of the statistical theory of dense gases and liquids.     

Effects of hydrogen bonds on solid state TATB,RDX,and DATB under high pressures

To probe the behavior of hydrogen bonds in solid energetic materials, we conduct ReaxFF and SCC-DFTB molecular dynamics simulations of crystalline TATB, RDX, and DATB. By comparing the intra- and inter-molecular hydrogen bond- ing rates, we find that the crystal structures are stabilized by inter-molecular hydrogen bond networks. Under high-pressure, the inter- and intra-molecular hydrogen bonds in solid TATB and DATB are nearly equivalent. The hydrogen bonds in solid TATB and DATB are much shorter than in solid RDX, which suggests strong hydrogen bond interactions existing in these energetic materials. Stretching of the C-H bond is observed in solid RDX, which may lead to further decomposition and even detonation.     

Cellular instabilities of expanding hydrogen/propane spherical flames at elevated pressures: theory and experiment

An experimental and theoretical investigation of the onset of cellular instabilities on spherically expanding flames in mixtures of hydrogen and propane in air at elevated pressures was conducted. Critical conditions for the onset of instability were measured and mapped out over a range of pressures and mixture compositions. An asymptotic theory of hydrodynamic and diffusional-thermal cell development on flames in mixtures comprised of two scarce fuels burning in air was also formulated. Predicted values of Peclet number, defined as the flame radius at the onset of instability normalized by the flame thickness, were shown to compare favorably with the experimentally measured values.     

Comparison between standard and counterpoise-corrected optimization using some hydrogen and halogen bonded systems

The effect of the counterpoise correction on the geometries, stabilization energies, and vibrational harmonic frequencies of some hydrogen- and halogen-bonded systems (B?=?CH₃CN,?HCN,?NH₃,?N₂,?CO,?H₂O,?H₂S,?PH₃;?HX?=?HF,?HCl,?HBr,?HCN,?HCF₃; XY?=?Br₂,?BrCl,?BrF,?Cl₂,?ClF,?F₂) has been analysed at the MP2 level of theory using the popular 6-311++G(d,p) basis set. The optimized B?···?H and B?···?X bond lengths increase with counterpoise (CP) correction. In some cases standard values and in other cases CP-corrected values are close to experimental data. The absolute values of complexation energies of CP-corrected structures are higher than standard by inclusion of BSSE correction. The effect of CP correction on intermolecular bond lengths and complexation energies of B?···?XY series are usually higher than B?···?HX. Also, this effect is higher for H₂S and PH₃ groups. The CP correction changes the vibrational harmonic frequencies by 0–100%. The changes are frequently lower than 20% for frequencies higher than 300?cm^?1.     

三种蛋白和黄酮结合物中氢键与黄酮稳定性相关性分析研究

运用三维荧光光谱、紫外可见分光光谱以及傅里叶红外光谱等手段研究了蛋白与黄酮分子的相互作用,并结合相关性分析的统计学手段分析了蛋白与黄酮分子相互作用方式对黄酮稳定性的影响。实验结果表明,疏水相互作用是三种蛋白与黄酮分子之间主要的作用力,在牛血清白蛋白与黄酮的结合中有氢键的参与,同时发现在牛血清白蛋白体系中黄酮的稳定性明显增强。通过相关性分析证明蛋白对黄酮稳定性的提高与两者之间的分子间氢键有关,氢键结合作用越强蛋白对黄酮保护越明显。