FCmini: Simple and Efficient Franck–Condon Simulations of Vibronic Spectra
- 1Chemistry, Loughborough Univeristy, Epinal Way, Loughborough, Leicestershire, United Kingdom, LE11 3TU
Abstract
Vibronic structure plays a crucial role in determining the shape and width of molecular absorption and emission spectra. Existing methods for modelling vibronic structure are often computationally demanding, and their results can be difficult to interpret. With this in mind, we present FCmini, a minimal model for simulating vibronic progressions in typical “well-behaved” organic molecules. The approach explicitly treats dominant modes via Franck–Condon theory while modelling the remaining modes through a semi-classical approximation. This hybrid strategy, implemented within our MATILDA toolbox, yields a computationally efficient method that provides transparent insight into which modes govern spectral features. We demonstrate the approach on two contrasting systems: anthracene as a benchmark molecule with a characteristic vibronic progression and mDICz as a narrowband emitter relevant to organic light emitting diode design. For anthracene, we show that its vibronic progression and even the fine structure of the peak shapes emerge using only a small subset of the vibrational modes. For mDICz, we accurately reproduce the remarkably low Stokes shift (<0.02 eV) and narrow spectral width (<0.08 eV). The efficiency of the method allows us to investigate a variety of methodological influences, including the effect of the density functional, the solvation model, and the Tamm-Dancoff approximation to TDDFT revealing that excitation energies, spectral shapes, intensities, and lifetimes all depend critically on these. Generally, we obtain good results for all quantities using the PBE0 functional in the full TDDFT formalism with implicit solvation. In summary, we believe that FCmini will present itself as a useful tool not only for spectra predictions but also for structure-property relations and methodological investigations.
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BibTeX
@misc{ghosh2026fcmini,
title = {{FCmini: Simple and Efficient Franck–Condon Simulations of Vibronic Spectra}},
author = {Sayan Ghosh and Giulia Woelfle Conway and Felix Plasser},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15008403/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008403/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - FCmini: Simple and Efficient Franck–Condon Simulations of Vibronic Spectra
AU - Sayan Ghosh
AU - Giulia Woelfle Conway
AU - Felix Plasser
PY - 2026
DA - 2026/09/07
PB - ChemRxiv
DO - 10.26434/chemrxiv.15008403/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008403/v1
AB - Vibronic structure plays a crucial role in determining the shape and width of molecular absorption and emission spectra. Existing methods for modelling vibronic structure are often computationally demanding, and their results can be difficult to interpret. With this in mind, we present FCmini, a minimal model for simulating vibronic progressions in typical “well-behaved” organic molecules. The approach explicitly treats dominant modes via Franck–Condon theory while modelling the remaining modes through a semi-classical approximation. This hybrid strategy, implemented within our MATILDA toolbox, yields a computationally efficient method that provides transparent insight into which modes govern spectral features. We demonstrate the approach on two contrasting systems: anthracene as a benchmark molecule with a characteristic vibronic progression and mDICz as a narrowband emitter relevant to organic light emitting diode design. For anthracene, we show that its vibronic progression and even the fine structure of the peak shapes emerge using only a small subset of the vibrational modes. For mDICz, we accurately reproduce the remarkably low Stokes shift (<0.02 eV) and narrow spectral width (<0.08 eV). The efficiency of the method allows us to investigate a variety of methodological influences, including the effect of the density functional, the solvation model, and the Tamm-Dancoff approximation to TDDFT revealing that excitation energies, spectral shapes, intensities, and lifetimes all depend critically on these. Generally, we obtain good results for all quantities using the PBE0 functional in the full TDDFT formalism with implicit solvation. In summary, we believe that FCmini will present itself as a useful tool not only for spectra predictions but also for structure-property relations and methodological investigations.
ER -