Time-Dependent Multiconfigurational Short-Range Density Functional Theory with Generalized Valence Bond Wave Functions.

Abstract

We present a theory and an efficient implementation of TD-GVB-srDFT, a time-dependent multiconfigurational range-separated density functional theory based on generalized valence bond perfect-pairing (GVB-PP) wave functions. In GVB-srDFT, dynamic correlation effects are incorporated via range-separation of the Coulomb potential, using tailored Kohn-Sham functionals of the density. The present implementation builds on our earlier work on TD-GVB [Hapka et al. J. Chem. Phys. 2022, 156, 174102], which employs direct Hessian techniques for both wave function optimization and linear response. We benchmark the performance of TD-GVB-srDFT for singlet and triplet excitation energies, as well as indirect spin-spin coupling constants (SSCCs). Compared to the underlying GVB-PP model, the method significantly improves excitation energies and achieves accuracy comparable to the complete active space variant, CAS-srDFT, with mean absolute deviations of 0.2 eV. The use of the generalized Tamm-Dancoff approximation (gTDA) is mandatory for reliable treatment of triplet excitations. For organic molecules, SSCCs computed with GVB-srDFT closely match those from CAS-srDFT and HF-srDFT results, whereas pure GVB-PP performs markedly worse than CASSCF for all coupling terms. Both GVB-srDFT and CAS-srDFT accurately reproduce fluorine-metal couplings in transition metal complexes, provided that gTDA is applied to singlet contributions.