Strange results for ionization energy

[Axel]

On Jul 22, 6:32 pm, aarondesk <aaro... at gmail.com> wrote:
> I'm trying to calculate the ionization potential and electron affinity
> of bulk rutile TiO2. It's just a simple test- remove or add an
> electron and get the energy.
>
> I find that the energy goes up when I add an electron, while goes down
> when I remove an electron. So, ionization potential (M -> M+ + e-) and
> electron affinity (M- -> M + e-) are both negative. This is opposite
> to the expected trend and would suggest that my material auto-ionizes,
> which I'm sure it doesn't. I've tested this with another planewave
> code and have gotten the same result.
>
> I've tested lone atoms in big cells and get the correct behavior.
>
> I guess these strange results may be due to the periodic boundary
> conditions (possibly interacting charges), or how the background
> compensating charge is treated.
>
> Any ideas on this?


try a (web) search for "Makov-Payne Correction". :)

cheers,
   axel.

>
> Aaron