Boundary effects in the three-dimensional Ising model

Simulations of the standard three-dimensional ising model with a variety of boundary conditions, for medium and large systems, are compared with field-theoretical predictions. In particular, setting boundary spins equal to zero is not the best approximation for the Dirichtet boundary condition of zero magnetization at the boundary. The simulations for the specific heat agree semiquantitatively with the field theory for periodic and Dirichtet boundary conditions.