Convergence of relativistic perturbation theory for the 1s2p states in low-Z heliumlike systems.

Abstract

In a recent paper, Plante et al. [Phys. Rev. A 49, 3519 (1994)] presented relativistic all-order many-body calculations for n=1 and n=2 states of heliumlike ions with nuclear charge in the range Z=3--100. They were, however, unable to obtain converged solutions for the $^{1}$${\mathit{P}}_{1}$ states for low Z (Z\ensuremath{\le}6). We demonstrate in the present work how application of the ``extended model space formulation'' by Lindgren [J. Phys. B 7, 2441 (1974)] leads to convergence also for these cases.