X-Ray Absorption Spectroscopy with ΔSCF/ROKS
Excited state orbital optimization with ΔSCF/ROKS permits accurate modeling of excited states at DFT cost.
Very effective for states that TDDFT either misses (double excitations) or catastrophically fails to model (charge-transfer, core excitations).
Square Gradient Minimization (SGM) can optimize excited state orbitals cheaply (at ground state scaling) and reliably (without collapsing to ground state orbitals).
Can be applied to large systems due to low computational cost. Features include:
Excitation energies, geometry optimizations, frequency calculations.
XAS (X-ray absorption) for both closed-shell and radical species, without the need to empirically shift the spectrum.