Assessment of the time correlation function-based approach for absorption spectrum calculations using time-dependent...

Area of Science:

• Computational Chemistry
• Spectroscopy
• Molecular Dynamics

Background:

• Quantum chemical (QC) methods predict spectral peak positions and intensities but miss broadening effects.
• Accurate spectral prediction is vital for understanding molecular electronic properties.

Purpose of the Study:

• To assess a time correlation function (TCF) based approach for predicting molecular absorption spectra, including broadening.
• To evaluate the impact of different TCF approximations on spectral shape prediction.
• To investigate the role of molecular rigidity in spectral broadening.

Main Methods:

• Integration of quantum chemical calculations with classical molecular dynamics simulations.
• Application of five hierarchical time correlation function (TCF) based spectral formulas.
• Analysis using Kubo's stochastic theory to link molecular fluctuations and spectral broadening.

Main Results:

• The TCF approach successfully predicts spectra with broadening effects.
• Approximation levels in TCF formulas yielded comparable results for rigid molecules (FLU) but significant deviations for flexible molecules (CST).
• Molecular flexibility, leading to rapid transition dipole moment fluctuations, causes discrepancies in spectral predictions for CST.

Conclusions:

• The TCF-based method offers a robust way to computationally predict molecular spectra, including broadening.
• Molecular rigidity is a critical factor influencing the accuracy of predicted spectral shapes.
• Understanding molecular dynamics is key to accurate spectral prediction.