A simple yet powerful upper bound for Coulomb integrals

The last decade has witnessed remarkable progress in the development and application of quantum chemistry [ 1,2 ] and readily available computer programs can now be used to study chemical systems which, until a few years ago, would have been considered prohibitively large. Moreover, there is every reason to believe that the next decade will be just as fruitful as the last. At present, the most computationally demanding step in well-implemented Hartree-Fock (HF) and density functional theory (DFT) calculations [ 31 #I is the treatment of the non-local electron-electron interactions which, within finite basis set methods [ 41, reduce to classical Coulomb integrals