Nonperturbative calculations of double photoionization of Ne: An R matrix with pseudostate-convergence study

The R matrix with pseudostate (RMPS) method has been employed to perform nonperturbative calculations of the total cross sections for single-photon double photoionization of ground-state Ne. A series of calculations was performed in which the number of pseudostates included in the close-coupling expansion was varied. Within the constraints of currently available massively parallel computers, we were able to achieve reasonably good convergence of the double photoionization cross section for Ne. The final RMPS results in both the length and the velocity gauges are compared to double photoionization cross sections determined from many-body perturbation-theory calculations and synchrotron measurements.