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