  A new estimator for three-center two-particle Coulomb integrals is presented.
Our estimator is exact for some classes of integrals and is much more efficient
than the standard Schwartz counterpart due to the proper account of distance
decay. Although it is not a rigorous upper bound, the maximum degree of
underestimation can be controlled by two adjustable parameters. We also give
numerical evidence of the excellent tightness of the estimator. The use of the
estimator will lead to increased efficiency in reduced-scaling one- and
many-body electronic structure theories.
