Dynamical screening of an endohedral atom

The present work is a generalization of the dynamical screening factor presented by Lo [J. Phys. B 40, 3973 (2007)] to consider an atom located at an arbitrary position within the fullerene. A more elaborate investigation into the case where the atom is located at the center is performed and compared with quantum-mechanical calculations for dynamical screening factors of Ar@C-60 [M. E. Madjet , Phys. Rev. Lett. 99, 243003 (2007)] and Mg@C-60 [H. S. Chakraborty , Phys. Rev. A 78, 013201 (2008)]. The pi and sigma plasmons of the fullerene are accounted for in a modified screening factor to improve correspondence with the quantum calculations. The spatial dependence of the screening factor was explored with Ar@C-60 and Ar@C-240 and found to depend significantly on the radial distance of the atom from the center of the fullerene. A spatial averaging of the screening factor is presented.