As mentioned before the values of the formula_37-matrix elements are not so large in comparison with the ionization energy because the potentials of neighboring atoms on the central atom are limited. If formula_37 is not relatively small it means that the potential of the neighboring atom on the central atom is not small either. In that case it is an indication that the tight binding model is not a very good model for the description of the band structure for some reason. The interatomic distances can be too small or the charges on the atoms or ions in the lattice is wrong for example.