[CP2K:1220] Strange results for ionization energy

Juerg Hutter hut... at pci.uzh.ch
Wed Jul 23 08:52:36 CEST 2008

Hi Aaron

in addition to Axels comment I would like to point out
that this system is far from trivial for common GGA
functionals. Check out the recent literature on the
effect of hybrid functionals and LDA + U approximations
on the stability of defects in TiO2.



Juerg Hutter                   Phone : ++41 44 635 4491
Physical Chemistry Institute   FAX   : ++41 44 635 6838
University of Zurich           E-mail: hut... at pci.uzh.ch
Winterthurerstrasse 190
CH-8057 Zurich, Switzerland

On Tue, 22 Jul 2008, aarondesk 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?
> Aaron
> >

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