Graphical representations and cluster algorithms for critical points   with fields
  A two-replica graphical representation and associated cluster algorithm is described that is applicable to ferromagnetic Ising systems with arbitrary fields. Critical points are associated with the percolation threshold of the graphical representation. Results from numerical simulations of the Ising model in a staggered field are presented. The dynamic exponent for the algorithm is measured to be less than 0.5. 
Oliver Redner (Tubingen), Jon Machta (UMASS) and Lincoln Chayes (UCLA)