Simple method for obtaining electron scattering phase shifts from energies of an atom in a cavity

We present a simple method for obtaining elastic scattering phase shifts and cross sections from precise ab initio many-body perturbation theory energies of atoms in variable cavities. This method does not require calculations of wave functions of continuum states, can be generalized to many atoms and ions, and is extremely convenient because existing codes developed for energy calculations can be used without modification. The high precision of the method and close agreement with experiment are illustrated on examples of e-Ar and e-Kr scattering. Correlations as well as relativistic corrections are systematically considered.