A practical issue arises when using Eq. 6 for large r. With v as the integration variable on the left hand side, as 2αr increases (for a fixed α), j 0 (2αrv) containing the sine function oscillates more within the envelop set by e -v 2 , so that a larger Gauss-Hermite degree (larger N GH ) is needed to satisfy Eq. 6 for a given ε. However, as Fig. shows, increasing N GH causes many of {v n } to land in the tails of e -v 2 that contribute negligibly to the integral in Eq. 6 (Fig. ). To remedy this, the SGT algorithm reduces α in powers of 2 for larger distances. However, as ε decreases, in addition to requiring large N GH , numerical precision issues arise for calculating v n and w n , which make Eq. 6 more difficult to satisfy.