1,790 research outputs found
Heat capacity of liquids: A hydrodynamic approach
We study autocorrelation functions of energy, heat and entropy densities
obtained by molecular dynamics simulations of supercritical Ar and compare them
with the predictions of the hydrodynamic theory. It is shown that the predicted
by the hydrodynamic theory single-exponential shape of the entropy density
autocorrelation functions is perfectly reproduced for small wave numbers by the
molecular dynamics simulations and permits the calculation of the
wavenumber-dependent specific heat at constant pressure. The estimated
wavenumber-dependent specific heats at constant volume and pressure,
and , are shown to be in the long-wavelength limit in good agreement
with the macroscopic experimental values of and for the studied
thermodynamic points of supercritical Ar.Comment: 8 pages, 5 figure
Ab initio molecular dynamics study of collective excitations in liquid HO and DO: Effect of dispersion corrections
The collective dynamics in liquid water is an active research topic
experimentally, theoretically and via simulations. Here, ab initio molecular
dynamics simulations are reported in heavy and ordinary water at temperature
323.15 K, or 50C. The simulations in heavy water were performed both
with and without dispersion corrections. We found that the dispersion
correction (DFT-D3) changes the relaxation of density-density time correlation
functions from a slow, typical of a supercooled state, to exponential decay
behaviour of regular liquids. This implies an essential reduction of the
melting point of ice in simulations with DFT-D3. Analysis of longitudinal (L)
and transverse (T) current spectral functions allowed us to estimate the
dispersions of acoustic and optic collective excitations and to observe the L-T
mixing effect. The dispersion correction shifts the L and T optic (O) modes to
lower frequencies and provides by almost thirty per cent smaller gap between
the longest-wavelength LO and TO excitations, which can be a consequence of a
larger effective high-frequency dielectric permittivity in simulations with
dispersion corrections. Simulation in ordinary water with the dispersion
correction results in frequencies of optic excitations higher than in DO,
and in a long-wavelength LO-TO gap of 24 ps (127 cm).Comment: 14 pages, 9 figure
Profiles of electrostatic potential across the water-vapor, ice-vapor and ice-water interfaces
Ice-water, water-vapor interfaces and ice surface are studied by molecular
dynamics simulations with the SPC/E model of water molecules having the purpose
to estimate the profiles of electrostatic potential across the interfaces. We
have proposed a methodology for calculating the profiles of electrostatic
potential based on a trial particle, which showed good agreement for the case
of electrostatic potential profile of the water-vapor interface of TIP4P model
calculated in another way. The measured profile of electrostatic potential for
the pure ice-water interface decreases towards the liquid bulk region, which is
in agreement with simulations of preferential direction of motion of Li
and F solute ions at the liquid side of the ice-water interface. These
results are discussed in connection with the Workman-Reynolds effect.Comment: 7 pages, 5 figure
A simple ansatz for the study of velocity autocorrelation functions in fluids at different timescales
A simple ansatz for the study of velocity autocorrelation functions in fluids
at different timescales is proposed. The ansatz is based on an effective
summation of the infinite continued fraction at a reasonable assumption about
convergence of relaxation times of the higher order memory functions, which
have a purely kinetic origin. The VAFs obtained within our approach are
compared with the results of the Markovian approximation for memory kernels. It
is shown that although in the "overdamped" regime both approaches agree to a
large extent at the initial and intermediate times of the system evolution, our
formalism yields power law relaxation of the VAFs which is not observed at the
description with a finite number of the collective modes. Explicit expressions
for the transition times from kinetic to hydrodynamic regimes are obtained from
the analysis of the singularities of spectral functions in the complex
frequency plane.Comment: 14 pages, 2 figure
Depletion potentials near geometrically structured substrates
Using the recently developed so-called White Bear version of Rosenfeld's
Fundamental Measure Theory we calculate the depletion potentials between a
hard-sphere colloidal particle in a solvent of small hard spheres and simple
models of geometrically structured substrates: a right-angled wedge or edge. In
the wedge geometry, there is a strong attraction beyond the corresponding one
near a planar wall that significantly influences the structure of colloidal
suspensions in wedges. In accordance with an experimental study, for the edge
geometry we find a free energy barrier of the order of several which
repels a big colloidal particle from the edge.Comment: 7 pages, 7 figure
In memory of Zinoviy Gurskii
On May 29, 2004 Professor Zinoviy Gurskii, one of the leading Ukrainian experts in the theory of metals and alloys, would be 60. Unfortunately, a heavy illness took away on January 28, 2004 the life of the noted scientist and remarkable person
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