354 research outputs found
Universality of Ionic Criticality: Size- and Charge-Asymmetric Electrolytes
Grand canonical simulations designed to resolve critical universality classes
are reported for :1 hard-core electrolyte models with diameter ratios
. For Ising-type behavior prevails.
Unbiased estimates of are within 1% of previous (biased)
estimates but the critical densities are 5 % lower. Ising character is
also established for the 2:1 and 3:1 equisized models, along with critical
amplitudes and improved estimates. For , however, strong
finite-size effects reduce the confidence level although classical and O criticality are excluded.Comment: 4 pages, 3 figure
Lattice Models of Ionic Systems
A theoretical analysis of Coulomb systems on lattices in general dimensions
is presented. The thermodynamics is developed using Debye-Huckel theory with
ion-pairing and dipole-ion solvation, specific calculations being performed for
3D lattices. As for continuum electrolytes, low-density results for sc, bcc and
fcc lattices indicate the existence of gas-liquid phase separation. The
predicted critical densities have values comparable to those of continuum ionic
systems, while the critical temperatures are 60-70% higher. However, when the
possibility of sublattice ordering as well as Debye screening is taken into
account systematically, order-disorder transitions and a tricritical point are
found on sc and bcc lattices, and gas-liquid coexistence is suppressed. Our
results agree with recent Monte Carlo simulations of lattice electrolytes.Comment: 25 pages, 3 figures, ReVTeX 4, Submitted to J. Chem. Phy
Screening in Ionic Systems: Simulations for the Lebowitz Length
Simulations of the Lebowitz length, , are reported
for t he restricted primitive model hard-core (diameter ) 1:1 electrolyte
for densi ties and .
Finite-size eff ects are elucidated for the charge fluctuations in various
subdomains that serve to evaluate . On extrapolation to the
bulk limit for the low-density expansions (Bekiranov and
Fisher, 1998) are seen to fail badly when (with ). At highe r densities rises above the Debye
length, \xi_{\text{D}} \prop to \sqrt{T/\rho}, by 10-30% (upto ); the variation is portrayed fairly well by generalized
Debye-H\"{u}ckel theory (Lee and Fisher, 19 96). On approaching criticality at
fixed or fixed , remains finite with
but displays a
weak entropy-like singularity.Comment: 4 pages 5 figure
How Multivalency controls Ionic Criticality
To understand how multivalency influences the reduced critical temperatures,
Tce (z), and densities, roce (z), of z : 1 ionic fluids, we study equisized
hard-sphere models with z = 1-3. Following Debye, Hueckel and Bjerrum,
association into ion clusters is treated with, also, ionic solvation and
excluded volume. In good accord with simulations but contradicting
integral-equation and field theories, Tce falls when z increases while roce
rises steeply: that 80-90% of the ions are bound in clusters near T_c serves to
explain these trends. For z \neq 1 interphase Galvani potentials arise and are
evaluated.Comment: 4 pages, 4 figure
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Ionic fluids: charge and density correlations near gas-liquid criticality
The correlation functions of an ionic fluid with charge and size asymmetry
are studied within the framework of the random phase approximation. The results
obtained for the charge-charge correlation function demonstrate that the
second-moment Stillinger-Lovett (SL) rule is satisfied away from the gas-liquid
critical point (CP) but not, in general, at the CP. However in the special case
of a model without size assymetry the SL rules are satisfied even at the CP.
The expressions for the density-density and charge-density correlation
functions valid far and close to the CP are obtained explicitely
Lattice Models of Ionic Systems with Charge Asymmetry
The thermodynamics of a charge-asymmetric lattice gas of positive ions
carrying charge and negative ions with charge is investigated using
Debye-H\"uckel theory. Explicit analytic and numerical calculations, which take
into account the formation of neutral and charged clusters and cluster
solvation by the residual ions, are performed for , 3 and 4. As charge
asymmetry increases, the predicted critical point shifts to lower temperatures
and higher densities. This trend agrees well with the results from recent Monte
Carlo simulations for continuum charge-asymmetric hard-sphere ionic fluids and
with the corresponding predictions from continuum Debye-H\"uckel theory.Comment: submitted to J.Chem.Phy
Discretization Dependence of Criticality in Model Fluids: a Hard-core Electrolyte
Grand canonical simulations at various levels, -20, of fine- lattice
discretization are reported for the near-critical 1:1 hard-core electrolyte or
RPM. With the aid of finite-size scaling analyses it is shown convincingly
that, contrary to recent suggestions, the universal critical behavior is
independent of (\grtsim 4); thus the continuum RPM
exhibits Ising-type (as against classical, SAW, XY, etc.) criticality. A
general consideration of lattice discretization provides effective
extrapolation of the {\em intrinsically} erratic -dependence, yielding
(\Tc^ {\ast},\rhoc^{\ast})\simeq (0.0493_{3},0.075) for the
RPM.Comment: 4 pages including 4 figure
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