X-Ray Absorption Spectroscopy with $\Delta$SCF/ROKS

XAS spectrum of thymine

\(\Delta\)SCF benchmark for double excitations \(\Delta\)SCF/ROKS ansätze enables KS-DFT calculations of excited states. Square Gradient Minimization (SGM) algorithm affords cheap (at the ground-state scaling) and reliable (without collapsing to ground-state orbitals) optimization of excited-state orbitals. Highlights:

  • Effective for states that TDDFT either misses (double excitations) or catastrophically fails to describe (charge-transfer, core excitations);

  • Computes XAS (X-ray absorption spectra) for closed-shell and radical species, without empirical shifts;

  • Can be used to compute excitation energies, optimized geometries, and frequencies;

  • Can be applied to large systems due to low computational cost.

RMSE of ROKS for K-edge core-excitation energies

*XAS of allyl radical *