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HF band gap (Read 2348 times)
Gerrit-Jan Linker
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HF band gap
23.03.11 at 06:53:21
 
HF band gap
 
To determine the band gap using HF theory one cannot just subtract the energy of the HOMO from the LUMO.  The HOMO is property optimised hower the LUMO is not. It is optimised 'looking inwards' to a neutral system wheras it should have been optimised against the positively charged ion.  
 
To calculate the band gap more properly at the HF level of theory the following formula can be used:
Eg,HF = E- + E+ - 2E0  
where
Eg,HF : The band gap at the HF level of theory
E- : The energy of the -1 charged system after relaxing orbitals
E+ : The energy of the ionised system after relaxing the orbitals
E0 : The energy of the neutral system
 
Actually the band gap should be reduced by Eexciton, the attraction energy between the hole and the excited electron of the exciton.
 
See also:
HF theory
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« Last Edit: 23.03.11 at 07:04:17 by Gerrit-Jan Linker »  

Gerrit-Jan Linker
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