Centroid molecular dynamics approach to the transport properties of liquid para-hydrogen over the wide temperature range

Fundamental transport properties of liquid para-hydrogen (p-H(2)), i.e., diffusion coefficients, thermal conductivity, shear viscosity, and bulk viscosity, have been evaluated by means of the path integral centroid molecular dynamics (CMD) calculations. These transport properties have been obtained over the wide temperature range, 14-32 K. Calculated values of the diffusion coefficients and the shear viscosity are in good agreement with the experimental values at all the investigated temperatures. Although a relatively large deviation is found for the thermal conductivity, the calculated values are less than three times the amount of the experimental values at any temperature. On the other hand, the classical molecular dynamics has led all the transport properties to much larger deviation. For the bulk viscosity of liquid p-H(2), which was never known from experiments, the present CMD has given a clear temperature dependence. In addition, from the comparison based on the principle of corresponding states, it has been shown that the marked deviation of the transport properties of liquid p-H(2) from the feature which is expected from the molecular parameters is due to the quantum effect.     

Computation of the properties of liquid neon, methane, and gas helium at low temperature by the Feynman-Hibbs approach

The properties of liquid methane, liquid neon, and gas helium are calculated at low temperatures over a large range of pressure from the classical molecular-dynamics simulations. The molecular interactions are represented by the Lennard-Jones pair potentials supplemented by quantum corrections following the Feynman-Hibbs approach. The equations of state, diffusion, and shear viscosity coefficients are determined for neon at 45 K, helium at 80 K, and methane at 110 K. A comparison is made with the existing experimental data and for thermodynamical quantities, with results computed from quantum numerical simulations when they are available. The theoretical variation of the viscosity coefficient with pressure is in good agreement with the experimental data when the quantum corrections are taken into account, thus reducing considerably the 60% discrepancy between the simulations and experiments in the absence of these corrections.     

EuS高压相变发其弹性和热力学性质

采用平面波赝势密度泛函理论,利用第一性原理的方法研究了EuS的晶体结构、高压相变以及弹性性质．计算结果和实验值以及前人利用不同计算模型得到的理论值相吻合．研究了EuS的弹性常数、弹性模量和弹性的各向异性等力学性质随压力变化的趋势．同时研究了泊松比、德拜温度及纵波和横波的弹性波速随压力的变化趋势．基于德拜模型,进而研究了EuS在0-800K和0-60GPa下相变前后的热膨胀系数、热熔、Gruneisen参数等热力学性质．     

Transport Properties of Simple Fluids from the Soft‐Core Double Yukawa Potential

The present work is concerned with checking a new and simple pair potential function (soft‐core double Yukawa potential) for noble gases by calculation of the transport properties. The viscosity, thermal conductivity and self diffusion coefficient in dilute gas limit in the temperature range of 298‐1400 K are calculated and agreement with the measurements is, in general, within the experimental error. A comparison of the calculated and experimental values of the viscosity, thermal conductivity and the diffusion coefficients yields an average absolute deviation of 0.5%, 1.5% and 1.2%, respectively. Also, the calculated transport properties from this potential have been compared with those calculations via the accurate experimental potential and also the corresponding state.     

Effect of temperature and composition on density,viscosity and thermal conductivity of fatty acid methyl esters from soybean,castor and Jatropha curcas oils

This work is focused on experimental determination of density, viscosity and thermal conductivity as a function of temperature and composition for fatty acid methyl esters (FAME) from soybean, castor and Jatropha curcas oils. Results show that an increase in temperature, over the range of (273 to 363) K, resulted in a decrease of all properties studied. FAME from soybean and J. curcas oils presented similar rheological behaviour, while FAME from castor oil presented higher values for density and viscosity. Density, dynamic viscosity and thermal conductivity data for all systems obtained here were correlated using empirical equations with good agreement between experimental and calculated values. Experimental data presented here may be useful as a database for specification purposes and equipment design and plant operation in the biodiesel industry.     

Elastoviscous properties of polyisobutylene. IV. Relaxation time spectrum and calculation of bulk viscosity

The elastoviscous behavior of polyisobutylene may be interpreted in terms of a mechanical model consisting of a distribution of Maxwell elements connected in parallel. The structure of this “generalized Maxwell model” is specified by the distribution of relaxation times of the component elements. The relaxation of stress curve of the material is directly related to the distribution of relaxation times, and general expressions for the bulk viscosities (tensile and shear) of such a system in terms of the distribution of relaxation times are readily obtained. A simple “box distribution” of relaxation times is described which can be used to approximate the relaxation behavior of polyisobutylene at the long-time end of the relaxation time spectrum, and in terms of which the expressions for bulk viscosity reduce to very simple form. The parameters specifying this distribution may be determined from experimental relaxation curves by a simple graphical method. Values of these parameters as a functions of molecular weight and temperature are computed, by use of these data. It is shown that bulk viscosity values calculated from relaxation data by this method are in good agreement with experimental values for both tensile and shear deformations, and for both unfractionated and fractionated polymers. Measurements of viscosity and of relaxation of stress can thus be directly correlated, and could be used in combination to characterize elastoviscous properties over wide ranges of molecular weight and temperature.     

Rheological Behavior of Titanium Dioxide Suspensions

The rheological properties of titanium dioxide dispersed in water are measured over a wide range of powder concentrations, temperatures, and pH values. The value of intrinsic viscosity of titanium dioxide measured with an Ubbelohde capillary viscometer is 3.55, which is useful for determining the shape and aggregation property of the particles. The yield stress and steady shear viscosity of titanium dioxide with broad and narrow particle size distributions were measured over a wide range of solid volume fractions on a Brabender rheometer. It is observed that the rheological properties of the suspensions are quite different due to the difference in particle size distributions. Quemada, Casson, and Zhou's models were used to fit the experimental data and useful parameters were obtained. Calculated data are also in good agreement with the experimental data. As expected, the shear viscosity and yield stress decrease with increasing temperature. But when the temperature is around 50 degrees C, yield stress increases with increasing temperature while shear viscosity exhibits a complex behavior. The phenomena are very interesting and special. The Peclet number was used to analyze the shear thickening behavior. Models were also used to describe the shear viscosity under different temperatures and the master plots of the reduced variables eta/eta(infinity) vs t(c)gamma; at different temperatures are superimposed, which means the agreement is fair and the models are suitable to describe the rheological properties of titanium dioxide suspensions. pH effects were investigated on a Rheometrics RFS-II rheometer and it was found that pH can change the surface charge of the particles, which also affects the rheological behavior. The pH at which maximum shear viscosity and yield stress occur is in concordance with the isoelectric point. Copyright 2001 Academic Press.     

Elastic, electronic and thermal properties of YSZ from first principles

First principles calculations were performed to investigate the elastic, electronic and thermal properties of 14% cubic yttria-stabilized zirconia (YSZ) using the pseudo potential plane-wave method within the gradient generalized approximation (GGA) for the exchange and correlation potential. Computed lattice constant parameters are in good agreement with the available experimental results. The three independent elastic constants were computed by means of the stress-strain method, indicating that 14% cubic YSZ is a mechanically stable structure. From the knowledge of the elastic constants, a set of related properties, namely bulk, shear modulus, Young’s modulus, sound velocity, Debye temperature, thermal capacity and minimum thermal conductivity are numerically estimated in the frame work of the Voigt-Reuss-Hill approximation for YSZ polycrystalline. The calculated bulk modulus, shear modulus, Young’s modulus, sound velocity, Debye temperature, thermal capacity and minimum thermal conductivity are in reasonable agreement with the available experimental and theory data. Density of states, charge density and Mulliken population analysis show that the 14% cubic YSZ is covalent and possess ionic character.     

Transport properties of CO2-expanded acetonitrile from molecular dynamics simulations

Carbon-dioxide-expanded liquids, which are mixtures of organic liquids and compressed CO2, are novel media used in chemical processing. The authors present a molecular simulation study of the transport properties of liquid mixtures formed by acetonitrile and carbon dioxide, in which the CO2 mole fraction is adjusted by changing the pressure, at a constant temperature of 298 K. They report values of translational diffusion coefficients, rotational correlation times, and shear viscosities of the liquids as function of CO2 mole fraction. The simulation results are in good agreement with the available experimental data for the pure components and provide interesting insights into the largely unknown properties of the mixtures, which are being recognized as important novel materials in chemical operations. We find that the calculated quantities exhibit smooth variation with composition that may be represented by simple model equations. The translational and rotational diffusion rates increase with CO2 mole fraction for both the acetonitrile and carbon dioxide components. The shear viscosity decreases with increasing amount of CO2, varying smoothly between the values of pure acetonitrile and pure carbon dioxide. Our results show that adjusting the amount of CO2 in the mixture allows the variation of transport rates by a factor of 3-4 and liquid viscosity by a factor of 8. Thus, the physical properties of the mixture may be tailored to the desired range by changes in the operating conditions of temperature and pressure.     

Calculation of the transport properties of carbon dioxide. III. Volume viscosity, depolarized Rayleigh scattering, and nuclear spin relaxation

Transport properties of pure carbon dioxide have been calculated from the intermolecular potential using the classical trajectory method. Results are reported in the dilute-gas limit for volume viscosity, depolarized Rayleigh scattering, and nuclear spin relaxation for temperatures ranging from 200 to 1000 K. Three recent carbon dioxide potential energy hypersurfaces have been investigated. Calculated values for the rotational collision number for all three intermolecular surfaces are consistent with the measurements and indicate that the temperature dependence of the Brau-Jonkman correlation is not applicable for carbon dioxide. The results for the depolarized Rayleigh scattering cross section and the nuclear spin relaxation cross section show that calculated values for the generally more successful potentials differ from the observations by 9% at about 290 K, although agreement is obtained for nuclear spin relaxation at about 400 K.     

Structural,elastic, electronic and thermal properties of the cubic perovskite-type BaSnO3

First-principles calculations are performed to investigate the structural, elastic, electronic and thermal properties of the cubic perovskite-type BaSnO₃. The ground-state properties are in agreement with experimental data. The independent elastic constants, C₁₁, C₁₂ and C₄₄, are calculated from direct computation of stresses generated by small strains. A linear pressure dependence of the elastic stiffnesses is found. From the theoretical elastic constants, we have computed the elastic wave velocities along [100], [110] and [111] directions. The shear modulus, Young's modulus, Poisson's ratio, Lamé’s coefficients, average sound velocity and Debye temperature are estimated in the framework of the Voigt-Reuss-Hill approximation for ideal polycrystalline BaSnO₃ aggregate. Using the sX-LDA for the exchange-correlation potential, the calculated indirect fundamental band gap value is in very good agreement with the measured one. The analysis of the site-projected l-decomposed density of states, charge transfer and charge density shows that the bonding is of ionic nature. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the temperature effect on the lattice constant, bulk modulus, thermal expansion coefficient, heat capacity and Debye temperature is calculated.     

The Relative Reduced Redlich-Kister and Herráez Equations for Correlating Viscosities of 1,4-Dioxane + Water Mixtures at Temperatures from 293.15 K to 323.15 K

Viscosity deviations from ideal mixing for 1,4-dioxane + water mixtures over the entire range of composition at temperatures of (293.15, 303.15 and 313.15) K and atmospheric pressure were calculated from experimental viscosity data presented in a previous work. The temperature range was extended to 323.15 K with data from the literature. This system exhibits very large positive deviations due to strong heteromolecular interactions and also due to size differences of the unlike molecules. The viscosity data as well as their corresponding relative functions were used to test the applicability of two correlative equations: the reduced Redlich-Kister equation and the recently proposed Herráez equation. These relative functions are important to reduce the effect of temperature and, consequently, to reveal the effects of different types of interactions. Their correlation abilities at different temperatures, and using different numbers of parameters, are discussed for the case of limited experimental data. Generally, good agreement between experimental and calculated data was obtained with both equations provided more than three parameters were employed.     

Gas phase chemical equilibrium in dinitrogen trioxide and dinitrogen tetroxide

The ideal gas chemical thermodynamic properties for NO, NO₂, N₂O₃, and N₂O₄ for the temperature range 50 to 5000 K were evaluated by the statistical thermodynamic method using the most recent molecular parameters. In the calculations for NO and NO₂, the effects of anharmonicity and vibration—rotation interaction were included. The contributions due to centrifugal distortion were also included for NO₂. For evaluation of the thermodynamic properties for N₂O₃ and N₂O₄ molecules, the rigid-rotor and harmonic-oscillator model were adopted. A free internal rotation was assumed for N₂O₃ and an internal rotation barrier height (V₂) of 1.58 kcal mol⁻¹ was derived for N₂O₄. The thermodynamic properties due to hindered internal rotation were clculated using a partition function formed by summation of internal rotation energy levels. The thermodynamic properties for two equilibrium mixtures: NO₂---N₂O₄ and N₂O₃---NO---NO₂---N₂O₄ were also calculated. The effects of temperature and pressure on heat capacities and compositions of these two mixtures are illustrated graphically and the calculated heat capacities and equilibrim constants are in good agreement with available experimental values.     

Attainable superheat of argon-helium, argon-neon solutions

The method of lifetime measurement has been used to investigate the kinetics of spontaneous boiling-up of superheated argon-helium and argon-neon solutions. Experiments were made at a pressure of p = 1.5 MPa and concentrations up to 0.33 mol% in the range of nucleation rates from 10 (4) to 10 (8) s (-1) m (-3). The homogeneous nucleation regime has been distinguished. With good agreement between experimental data and homogeneous nucleation theory in temperature and concentration dependences of the nucleation rate, a systematic underestimation by 0.25-0.34 K has been revealed in superheat temperatures over the saturated line attained by experiment as compared with theoretical values calculated in a macroscopic approximation. The revealed disagreement between theory and experiment is connected with the dependence of the properties of new-phase nuclei on their size.     

Prediction of the transport properties of a polyatomic gas

An ab initio molecular potential model is employed in this paper to show its excellent predictability for the transport properties of a polyatomic gas from molecular dynamics simulations. A quantum mechanical treatment of molecular vibrational energies is included in the Green and Kubo integral formulas for the calculation of the thermal conductivity by the Metropolis Monte Carlo method. Using CO₂ gas as an example, the fluid transport properties in the temperature range of 300–1000 K are calculated without using any experimental data. The accuracy of the calculated transport properties is significantly improved by the present model, especially for the thermal conductivity. The average deviations of the calculated results from the experimental data for self-diffusion coefficient, shear viscosity, thermal conductivity are, respectively, 2.32%, 0.71% and 2.30%.     

Viscosity of liquid Co–Sn alloys: thermodynamic evaluation and experiment

Shear viscosity measurements were performed for liquid Co–Sn alloys over a wide temperature range above the respective liquidus temperatures. A high temperature oscillating-cup viscometer was used. It was found experimentally that viscosity as a function of temperature obeys an Arrhenius law. The data were compared with calculated values, obtained from different thermodynamic approaches. A good agreement was found between experimental results and calculated ones by the Budai–Benkö–Kaptay model.     

Thermochemical properties of the HSO radical

Thermochemical properties of the HSO radical in the ideal gas state from 0 to 3000 K were calculated in the harmonic-oscillator, rigid-rotor approximation using recent spectroscopic data for the vibrational frequencies and heat of formation, and theoretical estimates of the molecular geometry.     

Prediction of self-diffusion coefficient and shear viscosity of water and its binary mixtures with methanol and ethanol by molecular simulation

Density, self-diffusion coefficient, and shear viscosity of pure liquid water are predicted for temperatures between 280 and 373 K by molecular dynamics simulation and the Green-Kubo method. Four different rigid nonpolarizable water models are assessed: SPC, SPC/E, TIP4P, and TIP4P/2005. The pressure dependence of the self-diffusion coefficient and the shear viscosity for pure liquid water is also calculated and the anomalous behavior of these properties is qualitatively well predicted. Furthermore, transport properties as well as excess volume and excess enthalpy of aqueous binary mixtures containing methanol or ethanol, based on the SPC/E and TIP4P/2005 water models, are calculated. Under the tested conditions, the TIP4P/2005 model gives the best quantitative and qualitative agreement with experiments for the regarded transport properties. The deviations from experimental data are of 5% to 15% for pure liquid water and 5% to 20% for the water + alcohol mixtures. Moreover, the center of mass power spectrum of water as well as the investigated mixtures are analyzed and the hydrogen-bonding structure is discussed for different states.