Spin-orbit coupling can be included in the TDDFT calculation of excitation energies for closed-shell molecules. Two methods can be used in ADF. The first one includes spin-orbit coupling as a perturbation to a scalar relativistic calculation of excitation energies. The second one includes spin-orbit coupling self-consistently in the ground state calculation. If spin-orbit coupling is large, the second one is more accurate, but is also more time-consuming.
Perturbative inclusion of spin-orbit coupling
