R2022: A DFT/MRCI Ansatz with Improved Performance for Double Excitations

Abstract

A reformulation of the combined density functional theory and multireference configuration interaction method (DFT/MRCI) is presented. Expressions for ab initio matrix elements are used to derive correction terms for a new effective Hamiltonian. On the example of diatomic carbon, the correction terms are derived, focusing on the doubly excited 1 Δ g state, which was problematic in previous formulations of the method, as were double excitations in general. The derivation shows that a splitting of the parameters for intra-and interorbital interactions is necessary for a concise description of the underlying physics. Results for 1 L a and 1 L b states in polyacenes and 1 A u and 1 A g states in mini-β-carotenoids suggest that the presented formulation is superior to former effective Hamiltonians. Furthermore, statistical analysis reveals that all the benefits of the previous DFT/MRCI Hamiltonians are retained. Consequently, the here presented formulation should be considered as the new standard for DFT/MRCI calculations.

Electron affinities and lowest triplet and singlet state properties of para-oligophenylenes (n = 3–5): theory and experiment

“…Root mean square deviations of the DFT/MRCI method are typically in the 200 meV range for organic molecules with a closed-shell ground state when the R2022 Hamiltonian is employed. 38…”

“…The minima of the excited singlet states were determined with time-dependent density functional theory (TDDFT), those of the triplet states with TDDFT in the Tamm-Dancoff approximation. Unless stated otherwise, all electronic excitation energies and molecular wavefunctions at the optimised geometries were calculated with the combined DFT and multireference configuration interaction (DFT/MRCI) method 36,37 employing the recently presented R2022 Hamiltonian 38 which is particularly well suited for extended psystems. DFT/MRCI is a semi-empirical multireference configuration interaction ansatz based on KS orbitals and orbital energies of a closed-shell BH-LYP functional 39,40 determinant.…”

“…Root mean square deviations of the DFT/MRCI method are typically in the 200 meV range for organic molecules with a closed-shell ground state when the R2022 Hamiltonian is employed. 38 3.3.1 para-Terphenyl (p3P). The agreement between the calculated and measured 0-0 energies is relatively good (Table 2).…”

Molecular design of phenazine-5,10-diyl-dibenzonitriles and the impact on their thermally activated delayed fluorescence properties

“…53 Solvation was considered with the COSMO model. 54 A DFT/MRCI computation was then performed with the R2022 Hamiltonian, 55 the tight parameter set and an energy selector of 0.8 E h . The starting wavefunction was computed including eight orbitals and eight electrons with single and double excitations.…”

MQM 2022: The 10th Triennial Conference on Molecular Quantum Mechanics

“…They find that extending the underlying one-electron basis set to include low-lying virtual orbitals significantly improves the representation of the original potential. Finally, a reformulation of a combined DFT/multireference configuration interaction (MRCI) approach is reported by Dombrowski and co-workers in the Marian group at the Heinrich-Heine-Universität Düsseldorf involving a new effective Hamiltonian using a splitting of parameters associated with intra- and interorbital interactions . Based on their statistical analysis of the performance of this new method, they recommend it be considered the new standard for such calculations.…”