Constrained Density Functional Theory and Its Application in Long-Range Electron Transfer.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Kohn-Sham density functional theory (DFT) is a powerful tool for electronic structure calculations.
• Studying systems with density constraints is crucial for understanding complex chemical phenomena.
• Previous methods for constrained DFT were limited in scope.

Purpose of the Study:

• To extend constrained DFT to systems with multiple density constraints.
• To apply the enhanced method to study long-range charge-transfer (CT) states.
• To validate the approach for systems exhibiting proton-coupled electron transfer.

Main Methods:

• Developed an efficient constrained DFT approach optimizing a constraining potential iteratively.
• Applied the method to model systems with varying donor-acceptor distances.
• Calculated potential-energy curves for donor and acceptor states in a model complex.

Main Results:

• The constrained DFT method successfully handles multiple density constraints.
• The approach is size-consistent, yielding correct long-range CT energies.
• Accurate 1/R dependence of CT energy was observed for finite donor-acceptor separations.
• Qualitative agreement with experimental data for a proton-coupled electron transfer model was achieved, estimating a reaction barrier of 7 kcal/mol.

Conclusions:

• Constrained DFT with multiple constraints offers an efficient and accurate approach for electronic structure calculations.
• The method is well-suited for studying charge-transfer states and related phenomena.
• This work provides a valuable computational tool for investigating complex chemical reactions.