[Pw_forum] add or remove electron energy

[Stefano de Gironcoli]

The electron affinity is the ionization potential of the negative ion. 
The fact that it is smaller than the ionization potential of the neutral 
ion is in the end due to the fact that it feels the el-el repulsion of 
one additional electron.

Or if you prefer, in Hartree-Fock theory,  Koopmans theorems say that I 
is  - E_HOMO and A is -E_LUMO and since, by definition, E_LUMO > E_HOMO  
=> I > A

stefano

kazempoor at ph.iut.ac.ir wrote:
> Dear Stefano
>
> I now that these are affinity and ionization, But I don't understand why ionization always is grater than affinity? I just want to know the physical reason.
>
>
>
> Thanks a lot
>
>
>
>
> Ali Kazempour
> Physics Department, Isfahn University of Technology
>
> ----- Original Message -----
> From: "Stefano de Gironcoli" <degironc at sissa.it>
> To: "PWSCF Forum" <pw_forum at pwscf.org>
> Sent: Monday, May 3, 2010 6:10:25 PM
> Subject: Re: [Pw_forum] add or remove electron energy
>
> it is the difference between electron affinity and ionization potential.
> stefano
>
> kazempoor at ph.iut.ac.ir wrote:
>   
>> Dear All
>> I add one electron to an isolated atom and the difference in E(n+1)-E(n)=-0.09 Ryd but when I remove an electron from this atom 
>> I got E(n)-E(n-1)=-0.349 Ryd.
>> what is the reason for this difference? I think that this behavior is same for every system.
>> Thanks a lot 
>> Ali Kazempour
>> Physics Department, Isfahan University of Technology
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