ABSTRACT
As we have seen in the previous chapter the Born approximation becomes invalid at energies below the Born threshold. To solve the scattering problem at these low energies we must calculate the phase shifts and use the exact expression for the scattering cross section (13-22). The potential is that of (13-1) and the electron density is calculated by whatever method is practical: Hartree-Fock, Hartree, Thomas–Fermi–Dirac or Thomas–Fermi.
