Reduced electronic spaces for modeling donor/acceptor interactions.

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Electron Transfer Theory

Background:

• Electron transfer (ET) processes are fundamental in chemistry and biology.
• Accurate calculation of coupling elements (H(DA)) is crucial for understanding ET rates.
• The generalized Mulliken Hush (GMH) model offers a framework for diabatic state formulation.

Purpose of the Study:

• To formulate and evaluate diabatic states and coupling elements within the GMH model.
• To assess the convergence and accuracy of the GMH model with increasing electronic state space size (n).
• To compare GMH results with experimental data and other theoretical approaches.

Main Methods:

• Utilized the generalized Mulliken Hush (GMH) model for diabatic state formulation.
• Employed an effective 1-electron Hamiltonian and Kohn-Sham orbitals/energies.
• Calculated coupling elements (H(DA)) and effective D/A separation distances (r(DA)) for variable state spaces (n=2-6).
• Performed calculations on three mixed-valence binuclear Ru complexes.

Main Results:

• The 2-state (2-st) model provides the most appropriate estimate of effective coupling.
• GMH 2-st coupling values are similar (within 15% rms deviation) to superexchange-corrected values from larger spaces.
• H(DA) remains quasi-invariant for n=2-6, indicating model convergence.
• Larger state spaces lead to more localized states and weaker coupling, approaching 'through space' interactions.

Conclusions:

• The 2-state GMH model is a reliable and computationally efficient method for estimating ET coupling.
• The model successfully reconciles different theoretical assertions regarding multistate frameworks in ET.
• Results provide insights into the role of bridge states in mediating donor-acceptor coupling.