Difference beetween methods

Hello

I'm trying to reproduce a paper on bandgaps for 2D lattices. These
authors report using a FEM method. I understand this approach is
different from the one that MPB uses. And so are the results. I get
very similar in shape dispersion diagrams but the bandgaps reported by
them are completely different. I thought it could be provoked for ther
lack of resolution of the simulation I ran, but the same results were
obtained. I also changed the cell size for the averaging and the block
size of the eigen solver but none of these parameters seemed to be the
reason of the discrepancy. I also thought it could be the difference
of the approaches to solve the eigenvalue problem, but I guess that a
given geometry must have a unique dispersion diagram. Numeric errors
are to be expected but I guess either one of us is doing something
wrong. Anyone has any clue?

Best regards