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Accurate simulation of electronic excited states of large chromophores is often difficult due to the computationally expensive nature of existing methods. Common approximations such as fragmentation methods that are routinely applied to ground-state calculations of large molecules are not easily applicable to excited states due to the delocalized nature of electronic excitations in most practical chromophores. Thus, special techniques specific to excited states are needed. Δ-SCF methods are one such approximation that treats excited states in a manner analogous to that for ground-state calculations, accelerating the simulation of excited states. In this work, we employed the popular initial maximum overlap method (IMOM) to avoid the variational collapse of the electronic excited state orbitals to the ground state. We demonstrate that it is possible to obtain emission energies from the first singlet (S1) excited state of many thousands of dye molecules without any external intervention. Spin correction was found to be necessary to obtain accurate excitation and emission energies. Using thousands of dye-like chromophores and various solvents (12,318 combinations), we show that the spin-corrected initial maximum overlap method accurately predicts emission maxima with a mean absolute error of only 0.27 eV. We further improved the predictive accuracy using linear fit-based corrections from individual dye classes to achieve an impressive performance of 0.17 eV. Additionally, we demonstrate that IMOM spin density can be used to identify the dye class of chromophores, enabling improved prediction accuracy for complex dye molecules, such as dyads (chromophores containing moieties from two different dye classes). Finally, the convergence behavior of IMOM excited state SCF calculations is analyzed briefly to identify the chemical space, where IMOM is more likely to fail.
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This content will become publicly available on June 1, 2026
Excited-state methods for molecular systems: Performance, pitfalls, and practical guidance
Proper theoretical descriptions of ground and excited states are critical for understanding molecular photophysics and photochemistry. Complex interactions in experimentally interesting molecular systems require multiple approximations of the underlying quantum mechanics to practically solve for various physical observables. While high-level calculations of small molecular systems provide very accurate excitation energies, this accuracy does not always extend to larger systems or other properties. Because of this, the “best” method to study new molecules is not always clear, leading many researchers to default to inexpensive and easy-to-use black-box methods. Unfortunately, even when these methods reproduce experimental excitation energies, it is not necessarily for the right reasons. Without accurate descriptions of the underlying physics, it becomes challenging to understand new classes of molecules. Consequently, predicted properties and their trends may not offer reliable mechanistic understanding. This review is targeted at beginners in computational chemistry who are interested in studying excited-state properties. A brief overview of common ground- and excited-state methods are covered for easy reference during the comparison of methods. The primary focus of this review is to compare the accuracy of these methods for several important classes of chromophores. The performance and accuracy of each method are explored to provide practitioners a road map on what methods work well for different molecular systems and identify further work that needs to be done in the field.
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- Award ID(s):
- 2310205
- PAR ID:
- 10625338
- Publisher / Repository:
- Chemical Physics Reviews
- Date Published:
- Journal Name:
- Chemical Physics Reviews
- Volume:
- 6
- Issue:
- 2
- ISSN:
- 2688-4070
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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