CCL: Ionization potential and Electron affinity of Donor-Acceptor system



 Sent to CCL by: "Rafal A. Bachorz"
 [rafal.bachorz~~chemie.uni-karlsruhe.de]
 Dear Agalya,
 
Can anyone tell me how to calculate ionization potential of donor and electron affinity of acceptor in donor-acceptor system?
 
In one journal in have seen, that they mentioned HOMO energy as the ionization potential of donor and LUMO energy as the electron affinity of acceptor.
 
That would be correct from the point of view of Koopmans theorem. Koopmans theorem sometimes works fine for ionization potentials, but it is almost always wrong about the electron affinity which is much more difficult to evaluate.
 
Is that the correct way of calculating ionization potential of donor and electron affinity of acceptor in donor-acceptor system?
 
I would say that it is a very crude approximation, but perhaps it is the only one way you can afford the calculation for you systems.
 
Probaly the most correct way is to use the definition of the quantities of you interest:
 EA=E_N-E_A
 IP=E_N-E_C
 
where E_N is the energy of the neutral, E_A is the energy of the anion and E_C is the energy of the cation.
 Have a good day,
 Rafal
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 www.bachorz.eu