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Strong electron correlation plays an important role in transition-metal and heavy-metal chemistry, magnetic molecules, bond breaking, biradicals, excited states, and many functional materials, but it provides a significant challenge for modern electronic structure theory. The treatment of strongly correlated systems usually requires a multireference method to adequately describe spin densities and near-degeneracy correlation. However, quantitative computation of dynamic correlation with multireference wave functions is often difficult or impractical. Multiconfiguration pair-density functional theory (MC-PDFT) provides a way to blend multiconfiguration wave function theory and density functional theory to quantitatively treat both near-degeneracy correlation and dynamic correlation in strongly correlated systems; it is more affordable than multireference perturbation theory, multireference configuration interaction, or multireference coupled cluster theory and more accurate for many properties than Kohn–Sham density functional theory. This perspective article provides a brief introduction to strongly correlated systems and previously reviewed progress on MC-PDFT followed by a discussion of several recent developments and applications of MC-PDFT and related methods, including localized-active-space MC-PDFT, generalized active-space MC-PDFT, density-matrix-renormalization-group MC-PDFT, hybrid MC-PDFT, multistate MC-PDFT, spin–orbit coupling, analytic gradients, and dipole moments. We also review the more recently introduced multiconfiguration nonclassical-energy functional theory (MC-NEFT), which is like MC-PDFT but allows for other ingredients in the nonclassical-energy functional. We discuss two new kinds of MC-NEFT methods, namely multiconfiguration density coherence functional theory and machine-learned functionals.
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This content will become publicly available on April 16, 2026
An investigation of contributors to the spin exchange interactions in organic pentacene–radical dyads using quasi-degenerate perturbation theory
Chromophore–radical (C–R) dyads are a promising class of molecules with potential applications in magnetometry, nuclear magnetic resonance and quantum sensing. Given the vast chemical space that is possible in these systems, computational studies are vital to aid in the rational design of C–R molecules with desired electronic and spin properties. Multireference perturbation theory (MRPT) calculations have been shown to be useful for rationalizing spin correlations in C–R dyads. In this work we apply quasi-degenerate perturbation theory, specifically QD-NEVPT2, for the prediction of vertical transition energies (VTEs) as well as spin-correlation parameters in three-spin-center pentacene–radical dyads containing up to 153 atoms. We find that QD-NEVPT2 performs well in the prediction of JTR, the magnetic coupling parameter between the excited-state triplet and the radical, but underestimates VTEs; this underestimation is attributed to variational averaging over different spin states and active space limitations, and we show that addressing these shortcomings reduces error. The calculated magnitudes and signs of JTR are rationalized through molecular symmetry, coupling distance, and π-structure considerations. The predicted signs of JTR are consistent with and explained via mechanisms of kinetic and potential spin-exchange, allowing for future functional design of magnetic organic molecules. The role of active space choice on VTE accuracy and predicted magnetic coupling is additionally explored.
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- Award ID(s):
- 2339355
- PAR ID:
- 10597782
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- Physical Chemistry Chemical Physics
- Volume:
- 27
- Issue:
- 16
- ISSN:
- 1463-9076
- Page Range / eLocation ID:
- 8052 to 8076
- Subject(s) / Keyword(s):
- chromophore-radical spin polarization photophysics quantum sensing
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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