Calculating absorption and fluorescence spectra for chromophores in solution with ensemble Franck-Condon methods

Area of Science:

• Computational Chemistry
• Spectroscopy
• Theoretical Chemistry

Background:

• Modeling molecular spectra requires accounting for vibronic and environmental effects.
• Accurate excited state electronic structure calculations are essential.
• Existing nuclear ensemble and Franck-Condon methods have limitations.

Purpose of the Study:

• To present and analyze simulated absorption and fluorescence spectra using combined ensemble-Franck-Condon approaches.
• To compare these novel methods against standard techniques and experimental data.
• To assess the accuracy and computational efficiency of different combined ensemble-Franck-Condon strategies.

Main Methods:

• Utilized combined ensemble-Franck-Condon approaches for spectral simulations.
• Employed configurations from ground and excited state ab initio molecular dynamics.
• Compared three distinct combined ensemble-Franck-Condon methods.

Main Results:

• An average finite-temperature Franck-Condon line shape approach yielded spectra nearly identical to direct summation but at one-fourth the computational cost.
• Analyzed the impact of spectral simulation methods and electronic structure theory on spectral line shapes and Stokes shifts.
• Successfully simulated spectra for three chromophore-solvent systems.

Conclusions:

• Combined ensemble-Franck-Condon methods are capable of simulating both absorption and fluorescence spectra.
• These methods provide a powerful and efficient tool for linear optical spectra simulation.
• The findings offer insights into spectral line shape and Stokes shift determinants.