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  3. Umbrella Sampling For Excited States Using A Semiempirical Method.

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Umbrella Sampling for Excited States Using a Semiempirical Method.

Dóra Vörös1,2, Hans Georg Gallmetzer1,3, Johannes C B Dietschreit1

  • 1Institute of Theoretical Chemistry, Faculty of Chemistry, University of Vienna, Währinger Straße 17, 1090 Vienna, Austria.

JACS Au
|June 26, 2026

View abstract on PubMed

Summary
This summary is machine-generated.

This study extends umbrella sampling to excited states, enabling detailed exploration of molecular relaxation pathways and identification of conical intersections. The method reveals free energy barriers and thermodynamic insights crucial for understanding photoisomerization.

Keywords:
conical intersectionexcited statesnonadiabatic dynamicsphotoisomerizationphotoswitchsemiempirical electronic structureumbrella sampling

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Area of Science:

  • Computational Chemistry
  • Photochemistry
  • Quantum Chemistry

Background:

  • Umbrella sampling is a key technique for exploring ground-state reaction pathways and molecular conformations.
  • Investigating excited-state dynamics is crucial for understanding photochemical processes.

Purpose of the Study:

  • To extend umbrella sampling to study excited-state relaxation pathways.
  • To develop a workflow for detailed analysis of excited-state mechanisms.
  • To locate and characterize conical intersections and assess their accessibility.

Main Methods:

  • Utilizing the energy gap between electronic states as a collective variable for excited-state umbrella sampling.
  • Applying the semiempirical multireference configuration interaction (MRCI) with the orthogonalization model 2 (OM2) method.
  • Combining potential energy surface scans, nonadiabatic dynamics, and excited-state umbrella sampling.

    • Main Results:

    • Successfully applied the method to a push-pull stilbene derivative (4-(N,N-dimethylamino)-4'-nitrostilbene).
    • Identified and characterized five distinct conical intersections for trans and cis isomers.
    • Determined free energy barriers for conical intersection accessibility and analyzed thermodynamic evolution along relaxation pathways.

    Conclusions:

    • The developed workflow provides a comprehensive approach to studying excited-state relaxation mechanisms.
    • Excited-state umbrella sampling is effective for locating conical intersections and assessing their thermodynamic accessibility.
    • The study offers insights into the key thermodynamic features governing photoisomerization processes.