By default the program tries to evaluate the electrostatic Coulomb interaction energy between the fragments in a molecule using the exact fragment charge densities. The implemented algorithm requires that all fragments are spherically symmetric. This is checked by the program by verifying that all fragments have been computed in atom symmetry. It that is not the case, an alternative method is applied, using the fitted charge densities of the atoms; this is an approximation with a small, but not insignificant error. The following key forces the program to apply the fit density approach even in the case of spherically symmetric fragments. This aspect applies only to the final bonding energy analysis, not to energy computations and their gradients within the automatic geometry optimizer. The purpose of this option is to simulate a previously existing situation where the electrostatic term in the bonding energy was computed from the fit density regardless of the fragments and their internal symmetries.
FITELSTAT
presence of this key in the input file triggers using the fit density.
