I need to compute the helicity modulus as a function of temperature for a three-dimensional X-Y model (see N.K. Kultanov, Yu.E. Lozovik, "The critical behavior of the 3D X-Y model and its relation with fractal properties of the vortex excitations"). I am resorting to using a Monte Carlo simulation because I cannot find a closed expression for the superfluid density in a 3-D MC model in the literature. I have written a simple Monte Carlo simulation and I am experiencing some problems, i.e. long thermalization times and noisy results even when averaging on a huge number of simulations.
Since my code is simple, are there any tricks I could use to make the computation more efficient? References and source code would be very much appreciated. I am primarily interested in the 3-D case, since my code seems to work well for the 2-D case.
If anyone is interested I've uploaded my code (in C) here: http://pastebin.com/ScrMEaQ8