67 research outputs found
Two-dimensional core-softened model with water like properties. Study by thermodynamic perturbation theory
Thermodynamic properties of the particles interacting through smooth version
of Stell-Hemmer interaction were studied using Wertheim's thermodynamic
perturbation theory. The temperature dependence of molar volume, heat capacity,
isothermal compressibility and thermal expansion coefficient at constant
pressure for different number of bonding sites on particle were evaluated. The
model showed water-like anomalies for all evaluated quantities, but
thermodynamic perturbation theory does not properly predict the dependence of
these properties at a fixed number of bonding points.Comment: 7 pages, 6 figure
Clustering in complex ionic liquids in two dimensions
Two-dimensional ionic liquids with single site anion and cation-neutral dimer
are studied by computer simulations and integral equation techniques, with the
aim of characterizing differences with single site anion-cation mixtures, and
also with three dimensional equivalents of both models, in order to see the
competition between the Coulomb interactions and the clustering restrictions
due to reduced dimension. We find that the addition of the neutral site to the
cation suppresses the liquid-gas transition which occurs in the case of the
monomeric Coulomb system. Instead, bilayer membrane type ordering is found at
low temperatures. The agreement between the structural correlations predicted
by theory and the simulation is excellent until very close to the no-solution
region predicted by the theory. These findings suggest various relations
between the nature of the clustering at low temperatures, and the inability of
the theory to enter this regionComment: 27 pages, 13 figure
Phase behavior of attractive and repulsive ramp fluids: Integral equation and computer simulation studies
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Using Relative Entropy to Find Optimal Approximations: an Application to Simple Fluids
We develop a maximum relative entropy formalism to generate optimal
approximations to probability distributions. The central results consist in (a)
justifying the use of relative entropy as the uniquely natural criterion to
select a preferred approximation from within a family of trial parameterized
distributions, and (b) to obtain the optimal approximation by marginalizing
over parameters using the method of maximum entropy and information geometry.
As an illustration we apply our method to simple fluids. The "exact" canonical
distribution is approximated by that of a fluid of hard spheres. The proposed
method first determines the preferred value of the hard-sphere diameter, and
then obtains an optimal hard-sphere approximation by a suitably weighed average
over different hard-sphere diameters. This leads to a considerable improvement
in accounting for the soft-core nature of the interatomic potential. As a
numerical demonstration, the radial distribution function and the equation of
state for a Lennard-Jones fluid (argon) are compared with results from
molecular dynamics simulations.Comment: 5 figures, accepted for publication in Physica A, 200
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