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For the computation of the Coulomb potential the program uses a large number of so-called fit integrals: the overlap integrals of a fit function with a product of two basis functions, where at least two of the involved three functions are centered on the same atom. In fact these are ordinary overlap integrals of STOs because the fit and basis functions are all STOs and a product of STOs on a center is itself also an STO.
Obviously, when the two involved atoms are far enough apart, such overlap integrals become negligibly small. All fit integrals are ignored (and not computed) that are smaller - according to a rough but reasonable estimate - than a preset threshold.
The value of this treshold can be set via input:
EPSFIT accfitint
The threshold for ignoring fit integrals is 10-accfitint. The default for accfitint is 4.0.