We performed numerical simulations of 2D and 3D Edwards-Anderson spin glass models by using the recently developed multicanonical ensemble. Our ergodicity times increase with the lattice size approximately as
V3. The energy, entropy and other physical quantities are easily calculable at all temperatures from a single simulation. Their finite size scalings and the zero temperature limits are also explored.
The statistics of domain walls for ground states of the 2D Ising spin glass with +1 and -1 bonds are studied for
L×L square lattices with
L≤20, and
x = 0.25 and 0.5, where
x is the fraction of negative bonds, using periodic and/or antiperiodic boundary conditions. Under these conditions, almost all domain walls have an energy
Edw equal to 0 or 4. The probability distribution of the entropy,
Sdw, is found to depend strongly on
Edw. The results for
Sdw when
Edw=4 agree with the prediction of the droplet model. Our results for
Sdw when
Edw=0 agree with those of Saul and Kardar. In addition, we find that the distributions do not appear to be Gaussian in that case. The special role of
Edw=0 domain walls is discussed, and the discrepancy between the prediction of Amoruso, Hartmann, Hastings and Moore and the result of Saul and Kardar is explained.