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Point charge embedding for ONIOM excited states calculations.
Alessandro Biancardi1, Jeremy Barnes1, Marco Caricato1
1Department of Chemistry, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, USA.
The Journal of Chemical Physics
|December 18, 2016
Summary
Hybrid quantum mechanical methods improve electronic spectra prediction for large molecules. Constrained-fitted charges enhance ONIOM (Our own N-layered Integrated molecular Orbital molecular Mechanics) calculations, with specific strategies excelling for transition energies or oscillator strengths.
Area of Science:
- Computational Chemistry
- Quantum Mechanics
- Spectroscopy
Background:
- Hybrid quantum mechanical methods are crucial for interpreting and predicting electronic spectra in large molecular systems.
- The ONIOM (Our own N-layered Integrated molecular Orbital molecular Mechanics) method is a widely used hybrid approach.
- Accurate electronic spectra prediction requires accounting for polarization effects from surrounding groups.
Purpose of the Study:
- To evaluate the performance of the ONIOM hybrid method for calculating transition energies and oscillator strengths.
- To investigate the impact of embedding the core region in a field of fixed point charges.
- To explore and optimize charge fitting strategies for electronic embedding to minimize overpolarization.
Main Methods:
- Utilized the ONIOM hybrid method for electronic spectra calculations.
- Employed fixed point charges to represent polarization effects from substituent groups.
- Developed and tested two constrained charge fitting strategies: EE(L1) and EE(L2).
- Investigated various charge definitions, focusing on minimizing overpolarization at layer boundaries.
Main Results:
- Electronic embedding with constrained-fitted charges generally improves ONIOM performance over non-embedded calculations.
- The EE(L2) charge fitting strategy demonstrated superior accuracy for transition energies.
- The EE(L1) charge fitting strategy showed better performance for oscillator strengths.
- Observed that fixed point charges may lack the flexibility to fully adapt to all system-specific polarization needs.
Conclusions:
- Constrained-fitted charges enhance the accuracy of ONIOM calculations for electronic spectra.
- Different charge fitting strategies (EE(L1) vs. EE(L2)) yield optimal results for different spectral properties (oscillator strengths vs. transition energies).
- Further refinements, potentially including polarization of the embedding field, may be necessary for comprehensive accuracy.
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