Optical spectra in the condensed phase: Capturing anharmonic and vibronic features using dynamic and static...

Area of Science:

• Theoretical Chemistry
• Computational Spectroscopy
• Condensed Matter Physics

Background:

• Simulating condensed phase optical spectra is crucial but challenging due to anharmonicity and dynamical effects.
• Existing simulation methods employ different approximations, impacting their ability to capture various physical regimes.
• Vibronic progressions and spectral asymmetry are key features that require accurate theoretical treatment.

Purpose of the Study:

• To rigorously assess the applicability of different theoretical methods for simulating optical absorption spectra in condensed phase systems.
• To compare the performance of the ensemble scheme, Franck-Condon method, and the ensemble zero-temperature Franck-Condon approach.
• To evaluate methods based on cumulant expansion and classical dynamics with quantum correction factors for approximating time correlation functions.

Main Methods:

• Ab initio molecular dynamics simulations were performed on models of chromophores in the condensed phase.
• The study focused on the ensemble scheme, Franck-Condon (FC) method, and ensemble zero-temperature FC approach.
• Methods derived from cumulant expansion of energy gap fluctuations were analyzed, including approximations using classical dynamics with quantum correction factors.

Main Results:

• The study provides insights into the applicability of various simulation methods across different physical regimes.
• The performance of the ensemble scheme, FC method, and ensemble zero-temperature FC approach in capturing spectral features was rigorously assessed.
• The ability of approximated time correlation functions to represent quantum dynamics was tested.

Conclusions:

• The findings offer guidance on selecting appropriate simulation methods for condensed phase optical spectra.
• The study highlights the strengths and limitations of different approaches in capturing anharmonicity and dynamical effects.
• Results indicate when methods can qualitatively and quantitatively reproduce condensed phase spectral features.