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Structure, energetics, and electronic coupling in the (TCNE2)-* encounter complex in solution: a polarizable
1Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973, USA.
The Journal of Physical Chemistry. B
|October 16, 2007
Summary
Solvation effects in polar solvents significantly alter molecular structures, promoting charge localization. Despite these changes, calculated electronic coupling (HDA) remains higher than experimental estimates, suggesting further molecular-level solvent modeling is needed.
Area of Science:
- Computational chemistry
- Physical chemistry
- Molecular modeling
Background:
- Donor/acceptor electronic coupling (HDA) in gas-phase calculations often exceeds experimental solution-phase estimates.
- Solvation is known to influence molecular structure and electronic properties.
Purpose of the Study:
- To investigate the impact of polar solvent environments on the structure and electronic coupling of a prototypical dyad (TCNE2-*).
- To extend the counterpoise (CP) correction to include fragment relaxation energies within the polarizable continuum model (PCM).
Main Methods:
- Employed the polarizable continuum model (PCM) to simulate solvation effects in polar solvents.
- Utilized TD-DFT, spin-projected MP2 (PUMP2), and state-averaged two-configuration SCF (SA-TCSCF) for electronic coupling calculations.
- Extended CP correction to incorporate fragment relaxation energies within the PCM framework.
Main Results:
- Solvation induces noticeable structural changes, promoting charge localization and reducing stabilization energy from -18 to -3 kcal/mol.
- Calculated HDA values in solution, for a given dimer structure, are comparable to gas-phase values.
- Even with PCM, calculated HDA remains significantly higher than experimental estimates.
Conclusions:
- Solvation plays a crucial role in structural reorganization and charge localization for polar dyads.
- Current computational models, including PCM, may not fully capture the intermolecular interactions governing HDA in solution.
- Further investigations using molecular-level solvent models are recommended to reconcile theoretical and experimental findings.
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