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Internal conversion rates from the extended thawed Gaussian approximation: Theory and validation.

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  • 1Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Emil-Fischer Str. 42, 97074 Würzburg, Germany.

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The Extended Thawed Gaussian Approximation (ETGA) accurately predicts molecular internal conversion rates in anharmonic systems. This new semiclassical method outperforms traditional harmonic models for non-radiative processes.

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Area of Science:

  • Computational Chemistry
  • Theoretical Chemistry
  • Molecular Dynamics

Background:

  • Accurate prediction of nonradiative rates is crucial for understanding molecular emissive properties.
  • Global harmonic models are widely used but limited by the harmonic approximation, affecting internal conversion rate calculations.
  • Development of more accurate semiclassical methods is needed for systems beyond harmonic potentials.

Purpose of the Study:

  • Introduce a novel time-dependent semi-classical Extended Thawed Gaussian Approximation (ETGA) for calculating nonradiative rates.
  • Evaluate the performance of ETGA against established adiabatic and vertical harmonic methods.
  • Assess ETGA's accuracy in anharmonic potential systems compared to exact quantum dynamics.

Main Methods:

  • Implementation of the time-dependent semi-classical Extended Thawed Gaussian Approximation (ETGA).
  • Systematic comparison of ETGA with adiabatic and vertical harmonic models.
  • Testing on Morse potentials with varying anharmonicity and a double well potential.

Main Results:

  • ETGA demonstrates capability in predicting internal conversion rates for anharmonic systems with significant energy gaps.
  • Global harmonic models show insufficiency in accurately simulating these anharmonic potentials.
  • Calculated rates from ETGA show good agreement with reference values from exact quantum dynamics.

Conclusions:

  • The Extended Thawed Gaussian Approximation (ETGA) offers a more accurate approach for calculating nonradiative rates in complex molecular systems.
  • ETGA overcomes the limitations of global harmonic models, particularly for anharmonic potentials.
  • This method provides a valuable tool for predicting photophysical properties like internal conversion rates.