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SITE CHARGES AND THE STRUCTURE OF AN AQUEOUS-SOLUTION OF ETHANOL - THEORETICAL AND COMPUTER-SIMULATION RESULTS
No full textNON-POLAR SOLUTE WATER PAIR CORRELATION-FUNCTIONS - A COMPARISON BETWEEN COMPUTER-SIMULATION AND THEORETICAL RESULTS
No full textCOMPARISONS BETWEEN THEORETICAL AND COMPUTER-SIMULATION RESULTS FOR SITE SITE CORRELATION-FUNCTIONS OF METHANE AND NORMAL-BUTANE IN WATER
No full textThermal conductivity of water: Molecular dynamics and generalized hydrodynamics results
No full textEquilibrium molecular dynamics simulations have been carried out in the microcanonical ensemble at 300 and 255 K on the extended simple point charge (SPC/E) model of water [Berendsen et al., J. Phys. Chem. 91, 6269 (1987)]. In addition to a number of static and dynamic properties, thermal conductivity lambda has been calculated via Green-Kubo integration of the heat current time correlation functions (CF's) in the atomic and molecular formalism, at wave number k=0. The calculated values (0.67 +/- 0.04 W/mK at 300 K and 0.52 +/- 0.03 W/mK at 255 K) are in good agreement with the experimental data (0.61 W/mK at 300 K and 0.49 W/mK at 255 K). A negative long-time tail of the heat current CF, more apparent at 255 K, is responsible for the anomalous decrease of lambda with temperature. An analysis of the dynamical modes contributing to lambda has shown that its value is due to two low-frequency exponential-like modes, a faster collisional mode, with positive contribution, and a slower one, which determines the negative long-time tail. A comparison of the molecular and atomic spectra of the heat current CF has suggested that higher-frequency modes should not contribute to lambda in this temperature range. Generalized thermal diffusivity D-T(k) decreases as a function of k, after an initial minor increase at k = k(min). The k dependence of the generalized thermodynamic properties has been calculated in the atomic and molecular formalisms. The observed differences have been traced back to intramolecular or intermolecular rotational effects and related to the partial structure functions. Finally, from the results we calculated it appears that the SPC/E model gives results in better agreement with experimental data than the transferable intermolecular potential with four points TIP4P water model [Jorgensen et al., J. Chem. Phys. 79, 926 (1983)], with a larger improvement for, e.g., diffusion, viscosities, and dielectric properties and a smaller one for thermal conductivity. The SPC/E model shares, to a smaller extent, the insufficient slowing down of dynamics at low temperature already found for the TIP4P water model
GENERALIZED HYDRODYNAMICS AND THE ACOUSTIC MODES OF WATER - THEORY AND SIMULATION RESULTS
No full textABINITIO CALCULATIONS AS A SOURCE OF INTERMOLECULAR POTENTIAL FUNCTIONS - ETHANOL-WATER WITH A MINIMAL BASIS SET
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LIBRATIONAL DYNAMICS OF WATER IN TERMS OF ANGULAR VELOCITY CORRELATION-FUNCTIONS AND ORIENTATIONAL STRUCTURE
No full textThe high frequency (librational) dynamics of water is studied by molecular dynamics simulation on the TIP4P model at 245 K. The single-molecule part of the hydrogen current is described by a combination of autocorrelation functions of components of the angular velocity along the principal axes of inertia of the molecules. The distinct part of the hydrogen current is represented by a sum of cross correlation functions of the same components. The spectrum of the self current is almost quantitatively reproduced by the sum of the spectra of two of these contributions. The first is that relative to the component along the axis normal to the molecular plane and the second along the axis normal to the dipole vector, in the molecular plane, both multiplied by a geometrical parameter of the molecule. In the case of the distinct part, the interparticle correlation function of the projection of the angular velocity over the same two axes is weighted by the dot product of the dipole moments of each pair of molecules. The agreement between the results obtained this way and according to the usual definition is qualitatively satisfactory. The axis normal to the dipole in the plane of the molecule turns out to be a favourite channel for the propagation of rotational correlations in the liquid. The analysis of hydrogen current in terms of rotational correlations allows to show that the transition from single-molecule to collective dynamics is essentially complete when clusters of two or three shells of neighbors are considered. A simple model of the distinct hydrogen current as a time-propagated self function is able to qualitatively account for all features of the spectra of both longitudinal and transverse current. The ratio of the transverse to longitudinal delay time is shown to be equal to the square root of the amplitude of the librational band of the dielectric spectrum
SOME PRELIMINARY-RESULTS FROM A MONTE-CARLO STUDY OF A DILUTE AQUEOUS-SOLUTION OF ETHANOL
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