  The one-parametric Wang-Landau (WL) method is implemented together with an
extrapolation scheme to yield approximations of the two-dimensional
(exchange-energy, field-energy) density of states (DOS) of the 3D bimodal
random-field Ising model (RFIM). The present approach generalizes our earlier
WL implementations, by handling the final stage of the WL process as an
entropic sampling scheme, appropriate for the recording of the required
two-parametric histograms. We test the accuracy of the proposed extrapolation
scheme and then apply it to study the size-shift behavior of the phase diagram
of the 3D bimodal RFIM. We present a finite-size converging approach and a
well-behaved sequence of estimates for the critical disorder strength. Their
asymptotic shift-behavior yields the critical disorder strength and the
associated correlation length's exponent, in agreement with previous estimates
from ground-state studies of the model.
