Constricted variational density functional theory for spatially clearly separated charge-transfer excitations.

Area of Science:

• Quantum Chemistry
• Computational Chemistry

Background:

• Constricted Variational Density Functional Theory (CV-DFT) is a robust method for calculating excitation energies.
• Accurate prediction of charge-transfer (CT) excitation energies is crucial in computational chemistry.

Purpose of the Study:

• To apply and analyze the CV-DFT method for predicting CT excitation energies in model systems.
• To investigate the charge-transfer behavior and the impact of orbital relaxation at large separation distances.

Main Methods:

• Application of the CV-DFT method to ethylene-tetrafluoroethylene (C2H4 × C2F4) and zincbacteriochlorin-bacteriochlorin (ZnBC-BC) complexes.
• Analysis of CV-DFT energies to understand charge-transfer behavior as a function of internuclear distance (R).
• Utilizing the relaxed version of CV(∞)-DFT (R-CV(∞)-DFT) to study orbital relaxation effects.

Main Results:

• The study elucidates the -1/R charge-transfer behavior in CV-DFT for systems at large separation distances.
• The importance of orbital relaxations is highlighted through the R-CV(∞)-DFT method.
• The effects of transition matrix optimization in RSCF-CV(∞)-DFT for large separations were investigated, with proposed gradient restrictions to prevent unwanted transition mixing.

Conclusions:

• CV-DFT provides valuable insights into charge-transfer excitation energies and behavior.
• Orbital relaxation is a critical factor for accurate predictions, especially at extended internuclear distances.
• The developed methods and restrictions enhance the reliability of CV-DFT for complex systems.