Non-Perturbative Theory for Dispersion Self-Energy of Atoms
  We go beyond the approximate series-expansions used in the dispersion theory of finite size atoms. We demonstrate that a correct, and non-perturbative, theory dramatically alters the dispersion selfenergies of atoms. The non-perturbed theory gives as much as 100% corrections compared to the traditional series expanded theory for the smaller noble gas atoms. 
Priyadarshini Thiyam, C. Persson, I. Brevik, Bo E. Sernelius, and   Mathias Bostr\"om
physics.atom-ph quant-ph