  We extend the tight distance-dependent estimator proposed by Hollman et al.
[J. Chem. Phys. 142, 154106 (2015)] for the three-center Coulomb integrals over
Gaussian atomic orbitals to handle the two-center case. We also propose minor
modifications of the original three-center estimator for the case of contracted
ket Gaussians and concentric bra Gaussians.
