Free-energy calculations with multiple Gaussian modified ensembles.

We present a Monte Carlo algorithm, which samples free energies of complex systems. Less probable configurations are populated with the help of a multitude of additional Gaussian weights and parallel tempering is used for efficient Monte Carlo moves within phase space. The algorithm is easily parallelized and can be applied to a wide class of problems. We discuss algorithmic performance for the case of low-temperature phase separation in two-dimensional and three-dimensional Ising models, where we determine the magnetic interface tension. Multiple Gaussian modified ensemble simulations, unlike multicanonical ensemble simulations do not require a priori knowledge of the free energy and are of similar efficiency as multicanonical ensemble and Wang-Landau simulations.

Minimal current phase and universal boundary layers in driven diffusive systems.

We investigate boundary-driven phase transitions in open driven diffusive systems. The generic phase diagram for systems with short-ranged interactions is governed by a simple extremal principle for the macroscopic current, which results from an interplay of density fluctuations with the motion of shocks. In systems with more than one extremum in the current-density relation, one finds a minimal current phase even though the boundaries support a higher current. The boundary layers of the critical minimal current and maximal current phases are argued to be of a universal form. The predictions of the theory are confirmed by Monte Carlo simulations of the two-parameter family of stochastic particle hopping models of Katz, Lebowitz, and Spohn and by analytical results for a related cellular automaton with deterministic bulk dynamics. The effect of disorder in the particle jump rates on the boundary layer profile is also discussed.

Extremal principle for the steady-state selection in driven lattice gases with open boundaries.

This paper investigates the steady states of one-dimensional driven lattice gases with open boundary conditions. It shows how the extremal principle proposed recently by Popkov and Schütz can be modified to apply to more general cases. Monte Carlo simulations are presented for a one-dimensional totally asymmetric simple exclusion process with nearest neighbor repulsion under parallel update as an example. The simulations enable one to guess the exact phase diagram for this particular lattice gas with deterministic bulk dynamics, by fitting the data to analytic formulas, which appear to be exact in the thermodynamic limit.