361 research outputs found
Single spin- and chiral-glass transition in vector spin glasses in three-dimensions
Results of Monte Carlo simulations of XY and Heisenberg spin glass models in
three dimensions are presented. A finite size scaling analysis of the
correlation length of the spins and chiralities of both models shows that there
is a single, finite-temperature transition at which both spins and chiralities
order.Comment: 5 pages, 5 figures. Replaced by published versio
Vortex glass transition in a frustrated 3D XY model with disorder
The anisotropic frustrated three dimensional (3D) XY model with disorder in
the coupling constants is simulated as a model of a point disordered
superconductor in an applied magnetic field. From a finite size scaling
analysis of the helicity modulus it is concluded that the data is consistent
with a finite temperature transition with isotropic scaling and the correlation
length exponent is found to be \nu=1.50+/-0.12, consistent with 3D gauge glass
universality.Comment: For additional information, see
http://www.tp.umu.se/~olsson/VortexGlass.htm
Thermodynamic Construction of an One-Step Replica-Symmetry-Breaking Solution in Finite Connectivity Spin Glasses
An one-step replica-symmetry-breaking solution for finite connectivity
spin-glass models with K body interaction is constructed at finite temperature
using the replica method and thermodynamic constraints. In the absence of
external fields, this construction provides a general extension of replica
symmetric solution at finite replica number to one-step
replica-symmetry-breaking solution. It is found that this result is formally
equivalent to that of the one-step replica-symmetry-breaking cavity method. To
confirm the validity of the obtained solution, Monte Carlo simulations are
performed for K = 2 and 3. The thermodynamic quantities of the Monte Carlo
results extrapolated to a large-size limit are consistent with those estimated
by our solution for K = 2 at all simulated temperatures and for K = 3 except
near the transition temperature.Comment: 11pages, 19 figures. Added content and references. Accepted to Phys.
Rev.
Equilibrium and off-equilibrium simulations of chiral-glass order in three-dimensional Heisenberg spin glasses
Spin-glass and chiral-glass orderings in three-dimensional Heisenberg spin
glasses are studied both by equilibrium and off-equilibrium Monte Carlo
simulations. Fully isotropic model is found to exhibit a finite-temperature
chiral-glass transition without the conventional spin-glass order. Although
chirality is an Ising-like quantity from symmetry, universality class of the
chiral-glass transition appears to be different from that of the standard Ising
spin glass. In the off-equilibrium simulation, while the spin autocorrelation
exhibits only an interrupted aging, the chirality autocorrelation persists to
exhibit a pronounced aging effect reminisecnt of the one observed in the
mean-field model. Effects of random magnetic anisotropy is also studied by the
off-equilibrium simulation, in which asymptotic mixing of the spin and the
chirality is observed.Comment: 15 pages including 8 figures, plain Tex, to appear in Computer
Simulation Studies in Condensed Matter Physics XI, Springer, 199
Study of a model for the folding of a small protein
We describe the results obtained from an improved model for protein folding.
We find that a good agreement with the native structure of a 46 residue long,
five-letter protein segment is obtained by carefully tuning the parameters of
the self-avoiding energy. In particular we find an improved free-energy
profile. We also compare the efficiency of the multidimensional replica
exchange method with the widely used parallel tempering.Comment: typos corrected, one figure adde
Population Annealing with Weighted Averages: A Monte Carlo Method for Rough Free Energy Landscapes
The population annealing algorithm introduced by Hukushima and Iba is
described. Population annealing combines simulated annealing and Boltzmann
weighted differential reproduction within a population of replicas to sample
equilibrium states. Population annealing gives direct access to the free
energy. It is shown that unbiased measurements of observables can be obtained
by weighted averages over many runs with weight factors related to the free
energy estimate from the run. Population annealing is well suited to
parallelization and may be a useful alternative to parallel tempering for
systems with rough free energy landscapes such as spin glasses. The method is
demonstrated for spin glasses.Comment: 9 pages, 5 figures; version 2 has improved figure 5 and new titl
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