Excited states using the simplified Tamm-Dancoff-Approach for range-separated hybrid density functionals: development and application.

The recently introduced sTDA methodology [S. Grimme, J. Chem. Phys., 2013, 138, 244104] to compute excitation spectra of huge molecular systems is extended to range-separated hybrid (RSH) density functionals. The three empirical parameters of the method which describe a screened two-electron interaction are obtained for some common RSH functionals (ωB97 family, CAM-B3LYP, LC-BLYP) from a fit to theoretical SCS-CC2 reference vertical excitation energies for a set of small to medium-sized chromophores. The method is cross-validated on a set of inter- and intramolecular charge transfer states and a set composed of typical valence transitions. Overall small deviations from reference data of only about 0.2-0.4 eV are found with best performance for CAM-B3LYP and ωB97X-D3. To demonstrate versatility and robustness of the new methodology, applications (the UV/Vis spectrum of the pyridine polymer and the ECD spectrum of (P)-[11]helicene) and frequently used charge transfer examples are discussed. In one case, 11 000+ excited electronic states of a system containing 330 atoms were calculated. We show that the asymptotically correct sTDA-RSH combination yields results often superior to those based on global hybrids and that it opens up new possibilities for the computation of excited states in materials science and bio-molecular systems.