Relativistic R-matrix close-coupling method based on the effective many-body Hamiltonian: Benchmarks on the electron-impact excitations of the Kr⁶⁺ ion

A relativistic R-matrix close-coupling method based on effective many-body Hamiltonians is employed to calculate the electron-impact excitations of intercombination transitions in the Kr⁶⁺ ion as benchmarks in the quest for accurate representation of the target and collisional states in multivalence-electron ions. The effective Hamiltonian in relativistic multireference many-body perturbation theory accurately accounts for short-range many-body interactions unaccounted for by limited configuration-interaction representations of the basis states. The R-matrix method is successfully applied to the near-threshold electron impact excitation of the 4s^2 1S→4s4p ³P intercombination transition in the zinclike krypton (Kr⁶⁺) ion, where the observed disagreement between the experimental absolute total cross sections dominated by dielectronic resonances and those predicted by using the Breit-Pauli and Dirac R-matrix methods reveals an inadequacy of the extant R-matrix close-coupling calculations in compact configuration-interaction representation of target states.