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Investigation of benzene-hexafluorobenzene dynamics in liquid binary mixtures

JOURNAL OF CHEMICAL PHYSICS 2005年第22期122卷 224508,1-15页

作者： Elola, MD Ladanyi, BM Colorado State Univ Dept Chem Ft Collins CO 80523 USA

The structure and microscopic dynamics of liquid mixtures of benzene and hexafluorobenzene at room temperature and several compositions have been studied by molecular-dynamics simulations. In this implementation we have rescaled the intermolecular H-F cross potential parameters obtained from the Lorentz-Berthelot combining rules, in order to avoid the substantial overestimation of the energy of mixing predicted by the model when the usual rules are employed. We found that a reduction in the strength of cross H-F interactions by 50% relative to the geometric mean is required in order to get a good agreement with experiments. Radial-angular pair-correlation functions between like and unlike species have been computed and analyzed, by comparing them with the correlations in the corresponding neat liquids. We have also studied the microscopic intermolecular momentum transfer, by computing the time correlation function between the initial velocity of a central molecule and later velocities of neighboring molecules. Structural and dynamical information extracted from the mentioned functions seem to be consistent with the picture of relatively long-lived benzene-hexafluorobenzene (Bz-Hf) complexes present in the mixtures, which would be responsible for the considerable perturbation of the structure in the first shell of like species, and would be moving within the liquid in a parallel face-to-face configuration. Using the tools developed originally to estimate hydrogen-bond lifetimes in liquids, we have computed the lifetimes of the Bz-Hf complexes as a function of the mixture composition, by two different methods: the direct time-averaging scheme and from the autocorrelation function of bond occupation numbers. The obtained lifetimes are strongly dependent on the scheme chosen to compute the characteristic times. We have obtained for the Bz-Hf dimer in solution, at room temperature, lifetimes in the range of 30-40 ps from averaging schemes and around 60-120 ps from autoco

关键词： time correlation functions Scheme Geometric mean Autocorrelation function Liquid mixtures hexafluorobenzene binary mixtures liquids initial velocity mean life positronium

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Charge fluctuations in the slave fermion representation of the t-J model-evidence for phase separation from loop corrections

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JOURNAL OF PHYSICS-CONDENSED MATTER 1996年第25期8卷 4495-4507页

作者： Rasul, JW Bai, YJ Physics Department University of Michigan Ann Arbor MI 48109-1120 USA

We investigate the charge density correlation function in the slave fermion representation of the two-dimensional t-J model using the self-consistent perturbation approach developed for that model by Li et al (1992 Phys. Rev. B 45 5428), which to lowest order in (t, J) gives a diagrammatic equivalent to the usual mean field theory. At the lowest order the equal-time correlation function (interpreted as the holon density correlation function) shows similar features to the results of recent high-temperature series calculations. However the loop corrections, representing scattering of holes by the antiferromagnetic spin fluctuations, lead to a divergent compressibility at low temperatures for low hole dopings (delta) and small J/t, which we interpret as indicating a tendency towards phase separation at a temperature t(2) delta/J.

关键词： time correlation functions Holes Slaves Fermions correlation function Spin fluctuations Loops Contraceptive Coil Phase separation

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Hyper-parallel algorithms for centroid molecular dynamics: Application to liquid para-hydrogen

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CHEMICAL PHYSICS LETTERS 1996年第3-4期262卷 415-420页

作者： Calhoun, A Pavese, M Voth, GA Department of Chemistry University of Pennsylvania Philadelphia PA 19104-6323 USA

Centroid molecular dynamics (CMD) calculations are performed on liquid para-hydrogen at low temperatures. The quantum mechanical velocity time correlation functions and self-diffusion constants are calculated at 14 and 25 K, and the self-diffusion constants compare well with experiment. The CMD calculation is done in a multi-tiered parallel, or ''hyper-parallel'' , manner that significantly extends the range of applications.

关键词： Formulation Density Solids diffusivity time correlation functions Constants self-diffusion charge modulation device parahydrogen

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Molecular collective dynamics in solid para-hydrogen and ortho-deuterium: The Parrinello-Rahman-type path integral centroid molecular dynamics approach

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JOURNAL OF CHEMICAL PHYSICS 2003年第2期119卷 953-963页

作者： Saito, H Nagao, H Nishikawa, K Kinugawa, K Kanazawa Univ Fac Sci Dept Computat Sci Kanazawa Ishikawa 9201192 Japan Nara Womens Univ Fac Sci Dept Chem Nara 6308506 Japan

The single-particle and collective dynamics of hydrogen/deuterium molecules in solid hcp para-hydrogen (p-H-2) and ortho-deuterium (o-D-2) has been investigated by using the path integral centroid molecular dynamics (CMD) simulations at zero-pressure and 5.4 and 5.0 K, respectively. For this purpose, we have newly unified the standard CMD method with the Parrinello-Rahman-Nose-Hoover-chain-type isothermal-isobaric technique. The phonon density of states have been obtained and the dynamic structure factors have been calculated to observe the phonon dispersion relations of both crystals. For solid p-H-2, the high energy edge of the phonon energies of solid p-H-2 is >13 meV, and the calculated phonon energies are significantly higher than those observed in Nielsen's previous neutron scattering experiments in the energy region >9 meV. The relationship between the present results and the data reported so far is discussed to resolve the outstanding controversy regarding the phonon energies in solid p-H-2. On the other hand, the excitation energies for solid o-D-2 are in fairly good agreement with those of the neutron experiments. The calculated isothermal compressibility of solid p-H-2 is found to be very close to the experimental result. (C) 2003 American Institute of Physics.

关键词： Liquid para-hydrogen time-correlation functions Neutron-scattering Lattice-dynamics Canonical ensemble Quantum dynamics Density Formulation Pressure Phonon time correlation functions Phonon Density of states phonon dispersion relations Centroid lattice dynamics Molecular Dynamics Canonical ensemble Solid Phonon energy Curvilinear integral charge modulation device

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Vibrational spectroscopy of dynamic interactions and relaxation processes in ionic systems

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SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2024年 322卷 124840页

作者： Gafurov, Malik M. Rabadanov, Kamil. Sh. Russian Acad Sci Dagestan Fed Res Ctr Analyt Ctr Collect Use MGadzhiev St 45 Makhachkala Russia

In recent years, there has been a boom in the publication of research results on ionic (electrolyte) systems used in the creation of electrochemical energy systems (batteries, supercapacitors, etc.). One of the alternative ways to obtain dynamic information in ionic systems is spectroscopic experiments, and the most valuable information on the behavior of condensed systems at picosecond and adjacent time intervals is provided by vibrational spectroscopy. The source of this information is the analysis of the shape and width of the lines in the vibrational spectra of ion systems. This review aims to systematize the theoretical and methodological aspects of the study of the dynamics of ion systems by vibrational spectroscopy.

关键词： Raman spectroscopy Vibrational relaxation Ionic systems Melt Glass Solutions time correlation functions Vibrational dephasing

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THEORETICAL RHEOLOGY OF SUSPENSIONS OF FERROMAGNETIC ROD-LIKE PARTICLES

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INTERNATIONAL JOURNAL OF THERMOPHYSICS 1989年第1期10卷 183-197页

作者： ALTENBERGER, AR DAHLER, JS UNIV MINNESOTA DEPT CHEM ENGNMINNEAPOLISMN 55455

We extend the linear response-like derivation of the generalized Navier-Stokes equation to non-Newtonian flows with rate of strain-dependent transport coefficients. We derive a time correlation function expression for the viscosity tensor and point out possible ambiguities in the operational definitions of viscosity coefficients. Our analysis is specific to a suspension of polar, rod-like ferromagnetic particles. A commentary is included about the approximations that lead from the time correlation function and the molecular definition of the viscosity tensor to the standard, Brownian dynamics model used in the theoretical rheology of suspensions. Some theoretical difficulties and logical inconsistencies are pointed out. Preliminary results for the transport coefficients of dilute suspension of magnetic rod-like particles are presented.

关键词： ferromagnetic suspensions non-Newtonian fluids rheology time correlation functions

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The Slowly Relaxing Local Structure Perspective of Protein Dynamics by NMR Relaxation

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ISRAEL JOURNAL OF CHEMISTRY 2014年第1-2期54卷 47-59页

作者： Meirovitch, Eva Bar Ilan Univ Mina & Everard Goodman Fac Life Sci IL-5290002 Ramat Gan Israel

NMR relaxation is a powerful method for elucidating structural dynamics. Standard stochastic dynamic models generate time correlation functions (TCFs) that feature physically well-defined parameters. We developed such a model, called the slowly relaxing local structure (SRLS) approach, for proteins. SRLS is a two-body (protein and probe) coupled-rotator approach. Given that the protein (featuring diffusion tensor, D-1) restricts the probe (featuring diffusion tensor, D-2), the two bodies are inherently coupled dynamically. This is substantiated by a local potential, u, associated with a local ordering tensor, S. SRLS allows for general tensorial properties of D-1, D-2, S and the magnetic NMR tensors, and a general form of u. The TCFs are multi-exponential, in accordance with the degree of generality of the various tensors. The traditional model-free (MF) method is based on a different conceptualization. According to it a mode-decoupling bi-exponential (one term for each rotator) TCF captures adequately the detectable features of structural dynamics. Hence, stochastic approaches are unnecessary. Here, we show that this (amply proven) oversimplification leads to physically vague constructs/composites as descriptors of structural dynamics. We illustrate misleading results obtained with MF when mode coupling, or S tensor asymmetry, dominate the analysis. Finally, we delineate the substantial advantage in using SRLS TCF as quantity to be compared with its atomistic molecular dynamicsbased counterpart.

关键词： molecular dynamics NMR relaxation proteins stochastic models time correlation functions

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COMMENT ON SYMMETRY PROPERTIES OF THE LINEAR ENSKOG KINETIC OPERATORS

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JOURNAL OF STATISTICAL PHYSICS 1989年第1-2期55卷 381-387页

作者： SZAMEL, G 1.Institute of Theoretical Physics Warsaw University 00-681 Warsaw Poland

The one-particle average consistent with the structure of the revised Enskog theory is introduced. Symmetry properties of the linear kinetic operators reflecting those of theN-particle pseudo-Liouville operators are d... 详细信息

关键词： time correlation functions kinetic theory hard spheres Enskog equation

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Water dynamics on the surface of the protein barstar

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PHYSICAL CHEMISTRY CHEMICAL PHYSICS 2012年第44期14卷 15393-15399页

作者： Carmen Moron, Maria Univ Zaragoza Inst Ciencia Mat Aragon ICMA Consejo Super Invest Cient Dept Fis Mat CondensadaFac Ciencias E-50009 Zaragoza Spain

Water plays a fundamental function in life and technology. To gain a deeper knowledge to the problem of the hydration of biomolecules, the dynamics of water around an 89-residue protein of interest in molecular recognition, cancer cell research and amyloid fibrils investigations is analyzed. The biomolecule is the ribonuclease inhibitor barstar wild-type. The dynamics of the protein and the 7430 water molecules of the bath in which it is immersed is monitored during a period of 7 ns by using all-atom molecular dynamics simulations. The results confirm the existence of multiple time scales in the dynamics of water (10(-1) to 10(3) ps) at the atomic level. That heterogeneity of residence times is not lost if the system of reference is just one atom of the inhibitor. The dehydration process of barstar is considered through the analysis of time correlation functions, obtaining an averaged decay time of tau = 84.0 +/- 0.3 ps. A power law distribution, with scaling exponent alpha = 0.57 +/- 0.04, suggests that this hydration water exhibits a scale free dynamics (with respect to the residence time of solvent molecules). Most of the water molecules located on the surface of the protein spend times smaller than the picosecond while only about 1% of them stay for periods of time on the nanosecond scale.

关键词： time correlation functions fundamental function Water Molecule dynamics Biomolecules residence time Protein barstar protein, Bacillus amyloliquefaciens Hydration

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NONANALYTIC DISPERSION-RELATIONS FOR CLASSICAL FLUIDS .2. GENERAL FLUID

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JOURNAL OF STATISTICAL PHYSICS 1975年第4期12卷 311-359页

作者： ERNST, MH DORFMAN, JR UNIV UTRECHT INST THEORET PHYSUTRECHTNETHERLANDS UNIV MARYLAND DEPT PHYS & ASTRONCOLLEGE PKMD UNIV MARYLAND INST FLUID DYNAM & APPL MATHCOLLEGE PKMD

The analytic structure of the hydrodynamic frequenciesz(k) for the sound, heat, and shear modes and of the hydrodynamic equations for a monatomic fluid are discussed on the basis of the mode-mode coupling theory. It is shown that the hydrodynamic frequencies depend on the wave numberk, for smallk, asz(k) = ak + bk 2 + $$z(k) = ak + bk^2 + \sum\nolimits_{n = 1}^\infty {c_n k^{3 - 2^{ - n} } } $$ and that some of the correlation functions that appear in the Fourier-Laplace transforms of the hydrodynamic equations contain branch point singularities. The implications of these results for the derivation of linear hydrodynamic equations, such as the Burnett equations, and for the long-time behavior of time correlation functions are discussed.

关键词： time correlation functions derivation time characteristic bifurcation point Laplace transform hydrodynamic equations Burnett equations Hydrodynamics

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