A Full-Relativistic B-Spline R-Matrix Method for Electron and Photon Collisions with Atoms and Ions

We have extended our $B$-spline $R$-matrix (close-coupling) method~[1] to fully account for relativistic effects in a Dirac-Coulomb formulation. Our numerical implementation of the close-coupling method enables us to construct term-dependent, non-orthogonal sets of one-electron orbitals for the bound and continuum electrons. This is a critical aspect for complex targets, where individually optimized one-electron orbitals can significantly reduce the size of the multi-configuration expansions needed for an accurate target description. Furthermore, core-valence correlation effets are treated fully {\it ab initio}, rather than through semi-empirical, and usually local, model potentials. The method will be described in detail and illustrated by comparing our theoretical predictions for e-Cs collisions with benchmark experiments for angle-integrated and angle-differential cross sections~[2], various spin-dependent scattering asymmetries~[3], and Stokes parameters measured in superelastic collisions with laser-excited atoms~[4]. [1]~O.~Zatsarinny, Comp. Phys. Commun. {\bf 174}, 273 (2006). [2]~W.~Gehenn and E.~Reichert, J. Phys. B~{\bf 10}, 3105 (1977). [3]~G.~Baum {\it et al.}, Phys. Rev. A~{\bf 66}, 022705 (2002) and {\bf 70}, 012707 (2004). [4]~D.S.~Slaughter {\it et al.}, Phys. Rev. A~{\bf 75}, 062717 (2007).