Relativistic time-dependent configuration-interaction singles method

In this work, a derivation and implementation of the relativistic time-dependent configuration interaction singles (RTDCIS) method is presented. Various observables for krypton xenon atoms obtained by RTDCIS are compared with experimental data alternative calculations. This includes energies occupied orbitals in Dirac-Fock ground state, Rydberg state energies, Fano resonances photoionization cross sections. Diagrammatic many-body perturbation theory, based on random phase approximation, used as benchmark excellent agreement between reported at Tamm-Dancoff level. Results from computed length gauge, here negative energy states can be omitted acceptable loss accuracy. A complex absorbing potential, that to remove photoelectrons far ion, implemented scalar potential validated RTDCIS. The methodology presented opens future studies strong-field processes, such attosecond transient absorption high-order harmonic generation, electron hole spin dynamics other effects described first principle via Dirac equation.