Pressure of Membrane between Walls

For a single membrane of stiffness kappa fluctuating between two planar walls of distance d, we calculate analytically the proportionality constant in the pressure law p proportional to T^2/kappa^2 d^3, in very good agreement with results from Monte Carlo simulations.Comment: Author Information under http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of paper also at http://www.physik.fu-berlin.de/~kleinert/kleiner_re277/preprint.htm

Multigrid Method versus Staging Algorithm for PIMC Simulations

We present a comparison of the performance of two non-local update algorithms for path integral Monte Carlo (PIMC) simulations, the multigrid Monte Carlo method and the staging algorithm. Looking at autocorrelation times for the internal energy we show that both refined algorithms beat the slowing down which is encountered for standard local update schemes in the continuum limit. We investigate the conditions under which the staging algorithm performs optimally and give a brief discussion of the mutual merits of the two algorithms.Comment: 11 pp. LaTeX, 4 Postscript Figure

Critical Exponents from General Distributions of Zeroes

All of the thermodynamic information on a statistical mechanical system is encoded in the locus and density of its partition function zeroes. Recently, a new technique was developed which enables the extraction of the latter using finite-size data of the type typically garnered from a computational approach. Here that method is extended to deal with more general cases. Other critical points of a type which appear in many models are also studied.Comment: 4 pages, 3 figure

Correlation Length From Cluster-Diameter Distribution

We report numerical estimates of correlation lengths in 2D Potts models from the asymptotic decay of the cluster-diameter distribution. Using this observable we are able to verify theoretical predictions for the correlation length in the disordered phase at the transition point for $q=10$, 15, and 20 with an accuracy of about $1$. This is a considerable improvement over previous measurements using the standard (projected) two-point function.Comment: 4 pages, PostScript, contribution to LATTICE95. See also http://www.cond-mat.physik.uni-mainz.de/~janke/doc/home_janke.htm

Parallel-tempering cluster algorithm for computer simulations of critical phenomena

In finite-size scaling analyses of Monte Carlo simulations of second-order phase transitions one often needs an extended temperature range around the critical point. By combining the parallel tempering algorithm with cluster updates and an adaptive routine to find the temperature window of interest, we introduce a flexible and powerful method for systematic investigations of critical phenomena. As a result, we gain one to two orders of magnitude in the performance for 2D and 3D Ising models in comparison with the recently proposed Wang-Landau recursion for cluster algorithms based on the multibondic algorithm, which is already a great improvement over the standard multicanonical variant.Comment: pages, 5 figures, and 2 table

Phase Transition Strength through Densities of General Distributions of Zeroes

A recently developed technique for the determination of the density of partition function zeroes using data coming from finite-size systems is extended to deal with cases where the zeroes are not restricted to a curve in the complex plane and/or come in degenerate sets. The efficacy of the approach is demonstrated by application to a number of models for which these features are manifest and the zeroes are readily calculable.Comment: 16 pages, 12 figure

Multibondic Cluster Algorithm

Inspired by the multicanonical approach to simulations of first-order phase transitions we propose for $q$-state Potts models a combination of cluster updates with reweighting of the bond configurations in the Fortuin-Kastelein-Swendsen-Wang representation of this model. Numerical tests for the two-dimensional models with $q=7, 10$ and $20$ show that the autocorrelation times of this algorithm grow with the system size $V$ as $\tau \propto V^\alpha$, where the exponent takes the optimal random walk value of $\alpha \approx 1$.Comment: 3 pages, uuencoded compressed postscript file, contribution to the LATTICE'94 conferenc

Monte Carlo Study of 8-State Potts Model on 2D Random Lattices

We study the effect of quenched coordination-number disorder of random lattices on the nature of the phase transition in the two-dimensional eight-state Potts model, which is of first order on regular lattices. We consider Poissonian random lattices of toroidal topology constructed according to the Voronoi/Delaunay prescription. Monte Carlo simulations yield strong evidence that the phase transition remains first order.Comment: 4 pages, PostScript, contribution to LATTICE95. See also http://www.cond-mat.physik.uni-mainz.de/~janke/doc/home_janke.htm