Added alternative calculation of Potential, by using meshgrid to interpolate the needed Unitcell->saved as loadPESspecial

weird stuff happening with basic reciprocal lattice spacing, had to change a lot

Normalise with respect to the number of particles

For the full configuration case, the normalisation factor is changed from the number of particles to the number of scattering centres.

correction of the Fourier transform

Update prepare_potential.m

 Minor modifications to sim_gle_nd, just set some lines with easier access for debugging.