Relaxation energy, charge-transfer transitions

Much of chemistry occurs in the condensed phase solution phase ET reactions have been a major focus for theory and experiment for the last 50 years. Experiments, and quantitative theories, have probed how reaction-free energy, solvent polarity, donor-acceptor distance, bridging stmctures, solvent relaxation, and vibronic coupling influence ET kinetics. Important connections have also been drawn between optical charge transfer transitions and thennal ET. 

The genesis of the failure of TDDFT can be traced to the fact that TDDFT is a linear response theory. When an excitation moves charge from one area in a molecule to another, both ends of that molecule will geometrically relax. While charge transfer between molecules can be well approximated by ground-state density functional calculations of the total energies of the species involved, TDDFT must deduce the correct transitions by... 

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