Fernández Pérez, Luis AntonioMartín Mayor, VíctorYllanes, D.2023-06-202023-06-20© 2008 Els2009-02-010550-321310.1016/j.nuclphysb.2008.07.009https://hdl.handle.net/20.500.14352/45067We present Tethered Monte Carlo, a simple, general purpose method of computing the effective potential of the order parameter (Helmholtz free energy). This formalism is based on a new statistical ensemble, closely related to the micromagnetic one, but with an extended configuration space (through Creutz-like demons). Canonical averages for arbitrary values of the external magnetic field are computed without additional simulations. The method is put to work in the two-dimensional Ising model, where the existence of exact results enables us to perform high precision checks. A rather peculiar feature of our implementation, which employs a local Metropolis algorithm, is the total absence, within errors, of critical slowing down for magnetic observables. Indeed, high accuracy results are presented for lattices as large as L = 1024.engjournal articlehttp://doi.org/10.1016/j.nuclphysb.2009.04.022http://www.sciencedirect.com/open access5351-73Monte CarloCritical phenomenaPhase transitionsIsing model.2-dimensional ising-modelQuantum-field theoriesMagnetic-fieldEvaporation/condensation transitionEquilibrium dropletsCritical-dynamicsSpin systemsSimulationsPercolationAlgorithmFísica (Física)Física-Modelos matemáticos22 Física