Application of the variational <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>R</mml:mi></mml:math>-matrix method for the Dirac equation to the Be atom

This paper presents an implementation of the noniterative eigenchannel $R$-matrix method for the Dirac equation. It includes a brief introduction, implementation details, and results for the photoionization cross section of the beryllium atom. Beryllium is a convenient test due to small but significant relativistic effects. Our calculation aligns with other $R$-matrix calculations and experiments. It observes the change in the Fano line shape of the $(2pnd){\phantom{\rule{0.16em}{0ex}}}^{1}P$ series and reveals a coupling between triplet and singlet series observable in the ground-state photoionization cross section.