Relativistic dynamical polarizability of hydrogen-like atoms
  Using the operator representation of the Dirac Coulomb Green function the analytical method in perturbation theory is employed in obtaining solutions of the Dirac equation for a hydrogen-like atom in a time-dependent electric field. The relativistic dynamical polarizability of hydrogen-like atoms is calculated and analysed. 
Le Anh Thu, Le Van Hoang, L I Komarov and T S Romanova