In general, each of the modified nuclear attraction integrals (NAIs)
involving the positron as an additional "nucleus" located at C can be
represented as a three-dimensional quadrature sum over phi, theta, and r.
The radial coordinate quadrature is broken up
into two ranges: 0-1 and 1-infinity. For the 1-infinity range, we invoke
the transformation r --> 1/t which maps to the range 0-1 for t.
We use Gauss-Legendre quadratures for all three coordinates with
typical values being nphi = 32, ntht = 32, and
nrad = 64. Thus, for each modified NAI we must perform two
65,536-pt Gauss-Legendre quadratures.
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