Case k m 3 ) for the operator z m 3 r -k between two s-orbitals with exponents β 1 = β 2 = 1 placed at r 1 = (0, 0, z 1 ) and r 2 = (0, 0, z 2 ) (see Ref. for the definition of the different cases). The z-coordinates of the orbitals are varied so that b = |β 1 r 1 + β 2 r 2 | > 0 or b = 0. A cutoff function with α = 50.0 and q = 2 was used. a Using analytic expressions from Refs. . b Using corrected analytic expressions from this work and Ref. . c Numerical evaluation of Eqn. (2).