Generally use * periodic boundary conditions*, where the lattice wraps
around on itself to form a torus. This has been shown to give the
smallest finite size effects.

But then must be careful that in measuring the correlation function,
can only take measurements to for a lattice of size **L**, since
a distance **n** is equivalent to a distance on a lattice that
wraps around on itself.

Paul Coddington, Northeast Parallel Architectures Center at Syracuse University, paulc@npac.syr.edu