  We introduce a generic, parallel Wang-Landau method that is naturally suited
to implementation on massively parallel, petaflop supercomputers. The approach
introduces a replica-exchange framework in which densities of states for
overlapping sub-windows in energy space are determined iteratively by
traditional Wang-Landau sampling. The advantages and general applicability of
the method are demonstrated for several distinct systems that possess discrete
or continuous degrees of freedom, including those with complex free energy
landscapes and topological constraints.
