Please, can anyone explain how formula (5) is obtained in J.J. Barton article ''Approximate translation of screened spherical waves" . Phys.Rew. A ,Vol.32,N2, 1985. ?
https://doi.org/10.1103/PhysRevA.32.1019
The same formula are given in the book Pendry J.B. "Low enrgy electron diffraction. The...