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). 

XAS of thymine
XAS Spectrum of Thymine
double excitations
ΔSCF benchmark for double 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.  

RMSE of ROKS for K-edge core excitation energies
XAS of allyl
XAS of allyl radical