Ref. only covers the case b = 0 when r 1 = r 2 = 0. However, as the erratum mentions, β 1 r 1 = -β 2 r 2 also leads to b = 0, i.e. when the centroid of the two Gaussian basis functions happens to coincide with the operator center. As b approaches 0, the working equations become unstable, since b appears in the denominator. There is no physical problem with this point, one just has to rearrange the equations, as we show below.