Method of obtaining a closed-form exact 3D scattering solution of the Schrödinger equation Nicolae Grama, Cornelia Grama and Ioan Zamfirescu Eur. Phys. J. Plus, 137 10 (2022) 1196 Published online: 29 October 2022 DOI: 10.1140/epjp/s13360-022-03399-8