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

*From*: "Rafal A. Bachorz"
<rafal.bachorz*|*chemie.uni-karlsruhe.de>
*Subject*: CCL: Ionization potential and Electron affinity of
Donor-Acceptor system
*Date*: Wed, 11 Oct 2006 08:34:31 +0200

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
--
www.bachorz.eu