228 research outputs found
Rare-Event Sampling: Occupation-Based Performance Measures for Parallel Tempering and Infinite Swapping Monte Carlo Methods
In the present paper we identify a rigorous property of a number of
tempering-based Monte Carlo sampling methods, including parallel tempering as
well as partial and infinite swapping. Based on this property we develop a
variety of performance measures for such rare-event sampling methods that are
broadly applicable, informative, and straightforward to implement. We
illustrate the use of these performance measures with a series of applications
involving the equilibrium properties of simple Lennard-Jones clusters,
applications for which the performance levels of partial and infinite swapping
approaches are found to be higher than those of conventional parallel
tempering.Comment: 18 figure
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
Criticality in confined ionic fluids
A theory of a confined two dimensional electrolyte is presented. The positive
and negative ions, interacting by a potential, are constrained to move on
an interface separating two solvents with dielectric constants and
. It is shown that the Debye-H\"uckel type of theory predicts that
the this 2d Coulomb fluid should undergo a phase separation into a coexisting
liquid (high density) and gas (low density) phases. We argue, however, that the
formation of polymer-like chains of alternating positive and negative ions can
prevent this phase transition from taking place.Comment: RevTex, no figures, in press Phys. Rev.
Multiple Histogram Method for Quantum Monte Carlo
An extension to the multiple-histogram method (sometimes referred to as the
Ferrenberg-Swendsen method) for use in quantum Monte Carlo simulations is
presented. This method is shown to work well for the 2D repulsive Hubbard
model, allowing measurements to be taken over a continuous region of
parameters. The method also reduces the error bars over the range of parameter
values due the overlapping of multiple histograms. A continuous sweep of
parameters and reduced error bars allow one to make more difficult
measurements, such as Maxwell constructions used to study phase separation.
Possibilities also exist for this method to be used for other quantum systems.Comment: 4 pages, 5 figures, RevTeX, submitted to Phys. Rev. B Rapid Com
Criticality in polar fluids
A model of polar fluid is studied theoretically. The interaction potential,
in addition to dipole-dipole term, possesses a dispersion contribution of the
van der Waals-London form. It is found that when the dispersion force is
comparable to dipole-dipole interaction, the fluid separates into coexisting
liquid and gas phases. The calculated critical parameters are in excellent
agreement with Monte Carlo simulations. When the strength of dispersion
attraction is bellow critical, no phase separation is found.Comment: 5 pages, 2 figures, references modifie
Asymmetric Fluid Criticality II: Finite-Size Scaling for Simulations
The vapor-liquid critical behavior of intrinsically asymmetric fluids is
studied in finite systems of linear dimensions, , focusing on periodic
boundary conditions, as appropriate for simulations. The recently propounded
``complete'' thermodynamic scaling theory incorporating pressure
mixing in the scaling fields as well as corrections to scaling
, is extended to finite , initially in a grand
canonical representation. The theory allows for a Yang-Yang anomaly in which,
when , the second temperature derivative,
, of the chemical potential along the phase
boundary, , diverges when T\to\Tc -. The finite-size
behavior of various special {\em critical loci} in the temperature-density or
plane, in particular, the -inflection susceptibility loci and the
-maximal loci -- derived from where -- is carefully elucidated and
shown to be of value in estimating \Tc and \rhoc. Concrete illustrations
are presented for the hard-core square-well fluid and for the restricted
primitive model electrolyte including an estimate of the correlation exponent
that confirms Ising-type character. The treatment is extended to the
canonical representation where further complications appear.Comment: 23 pages in the two-column format (including 13 figures) This is Part
II of the previous paper [arXiv:cond-mat/0212145
A Multiscale Approach to Determination of Thermal Properties and Changes in Free Energy: Application to Reconstruction of Dislocations in Silicon
We introduce an approach to exploit the existence of multiple levels of
description of a physical system to radically accelerate the determination of
thermodynamic quantities. We first give a proof of principle of the method
using two empirical interatomic potential functions. We then apply the
technique to feed information from an interatomic potential into otherwise
inaccessible quantum mechanical tight-binding calculations of the
reconstruction of partial dislocations in silicon at finite temperature. With
this approach, comprehensive ab initio studies at finite temperature will now
be possible.Comment: 5 pages, 3 figure
Nondielectric long-range solvation of polar liquids in cubic symmetry
Long-range solvation properties of strongly coupled dipolar systems simulated using the Ewald and reaction field methods are assessed by using electric fluctuation formulas for a dielectric medium. Some components of the fluctuating electric multipole moments are suppressed, whereas other components are favored as the boundary of the simulation box is approached. An analysis of electrostatic interactions in a periodic cubic system suggests that these structural effects are due to the periodicity embedded in the Ewald method. Furthermore, the results obtained using the reaction field method are very similar to those obtained using the Ewald method, an effect which we attribute to the use of toroidal boundary conditions in the former case. Thus, the long-range solvation properties of polar liquids simulated using either of the two methods are nondielectric in their character. (C) 2009 American Institute of Physics. [doi:10.1063/1.3250941
Multicanonical Multigrid Monte Carlo
To further improve the performance of Monte Carlo simulations of first-order
phase transitions we propose to combine the multicanonical approach with
multigrid techniques. We report tests of this proposition for the
-dimensional field theory in two different situations. First, we
study quantum tunneling for in the continuum limit, and second, we
investigate first-order phase transitions for in the infinite volume
limit. Compared with standard multicanonical simulations we obtain improvement
factors of several resp. of about one order of magnitude.Comment: 12 pages LaTex, 1 PS figure appended. FU-Berlin preprint FUB-HEP 9/9
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