K-Shell photoabsorption in Si11+: Relativistic contributions via Breit-Pauli R-matrix calculations

As a part of the investigation of the entire Si isonuclear sequence for x-ray spectral diagnostics, we focus on the Li-like Si11+ ion, a stable component that features prominently in x-ray astrophysical spectra. We perform R-matrix calculations for the photoabsorption cross section of Si11+ including relativistic contributions via the use of a Breit-Pauli Hamiltonian. Relativistic effects-predominantly spin-orbit splitting of resonances and mass-velocity and one-body Darwin global shifts of energies -are shown to be tractable and of importance for accuracy in x-ray spectral modeling data banks.