[Wien] Bad formation energies for the charged vacancies

[Laurence Marks]

Please see the next email on the list:
http://zeus.theochem.tuwien.ac.at/pipermail/wien/2007-January/008713.html

I think this is right and you take V0 from case.output0 (it is printed
there). You should do an empty cell test (no electrons) to verify this
and the units of V0, perhaps also looking at the code itself -- and
remember to check the limit as the distance between atoms gets large.


On Wed, Feb 24, 2010 at 11:05 AM, Yurko Natanzon
<yurko.natanzon at gmail.com> wrote:
> Dear Wien2k users and developers,
> I'd like to refresh the discussion about the total energies of the
> charged cells which took place three years ago:
> http://zeus.theochem.tuwien.ac.at/pipermail/wien/2007-January/008711.html
>
> I'm trying to calculate the formation energy of the Hydrogen vacancy
> in +/-1 charge states and find that the results are bad (much differ
> from the literature) although the formation energy of the neutral
> hydrogen vacancy is good. So my question arises if we can trust the
> values of the total energies for the charged cells in the recent
> version of Wien2k?
>
> To investigate this issue further I have performed the following
> tests: I've done the calculations of the total energy of Mg, MgH2 and
> GaN for three cases: neutral cell, cell with one electron removed (+1
> charge) and a cell with an electron added (-1 charge). The results
> were compared with the same calculation with another plane-wave code
> and are the following:
> -----------------------------------------
> hcp Mg:
> Wien2k:
> E(+1)-E(0) = 0.245 Ry
> E(-1)-E(0) = -0.199 Ry
>
> Plane-Wave code:
> E(+1)-E(0) = -0.226 Ry
> E(-1)-E(0) = 0.281 Ry
>
> bcc MgH2
> Wien2k:
> E(+1)-E(0) = 0.277 Ry
> E(-1)-E(0) = 0.085 Ry
>
> Plane-Wave code:
> E(+1)-E(0) = 0.024 Ry
> E(-1)-E(0) = 0.326 Ry
>
> fcc GaN
> Wien2k:
> E(+1)-E(0) = 1.12 Ry
> E(-1)-E(0) = -0.717 Ry
>
> Plane-Wave code:
> E(+1)-E(0) = -0.151 Ry
> E(-1)-E(0) = 0.443 Ry
> -------------------------------------------------
>
> In wien2k the charged cell was created by changing the number of
> electrons in case.in2 and adding the corresponding background charge
> in case.inm. One can observe, that the energies have the same order of
> magnitude, but the sequence of energies E(+1), E(0) and E(1) is
> inverse. It seems, that the system with +1 charge (electron removed)
> behaves like the system with -1 charge in the Plane-Wave code. Of
> course, the results of tests are not physical, because no supercell
> was used and no geometric relaxation was performed (however, it is not
> needed for Mg), but if one tries to do all the supercell and
> relaxation stuff and tries to calculate the defect formation energy,
> the result will be the same.
>
> I'd be grateful if you comment on this and suggest any corrections
> which should be provided to the total energies for the charged cells.
>
> with kind regards,
> Yurko
>
>
> --
> Yurko (aka Yuriy, Iurii, Jurij etc) Natanzon
> PhD student
> Department for Structural Research (NZ31)
> Henryk Niewodniczański Institute of Nuclear Physics
> Polish Academy of Sciences
> ul. Radzikowskiego 152,
> 31-342 Krakow, Poland
> E-mail: Yurii.Natanzon at ifj.edu.pl, yurko.natanzon at gmail.com
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
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>



-- 
Laurence Marks
Department of Materials Science and Engineering
MSE Rm 2036 Cook Hall
2220 N Campus Drive
Northwestern University
Evanston, IL 60208, USA
Tel: (847) 491-3996 Fax: (847) 491-7820
email: L-marks at northwestern dot edu
Web: www.numis.northwestern.edu
Chair, Commission on Electron Crystallography of IUCR
www.numis.northwestern.edu/
Electron crystallography is the branch of science that uses electron
scattering and imaging to study the structure of matter.