[Wien] Bad formation energies for the charged vacancies

Wed Feb 24 22:58:58 CET 2010

Did you try (from one of Freeman's papers I believe):

-Q*V_0(Q)/2 where Q is the excess charge of the cell (-ve for a
negative cell) and V_0(Q) is the vacuum Coulomb potential in the
calculation which is a function of Q which will depend upon the RMT.

Note the factor of 2. I don't think this is in Wien2k at the moment,
it needs to be added retroactively (or could in principle be added to
the code). It is a long time ago and I seem to remember that this
worked for the empty cell test, but no longer have the data, so....

On Wed, Feb 24, 2010 at 3:18 PM, Peter Blaha
<pblaha at theochem.tuwien.ac.at> wrote:
> I've started some tests after the first query and it seems we might miss a
> term in the total
> energy.
>
> I created a clmsum-file (density) which is constant and is normalized to one
> and put this into
> a cell with a single H nucleus.
> So it refers to the test case of a H+ ion in a lattice, where I do not add a
> constant background, but
> put the "background charge into case.clmsum.
>
> When one switches off the XC-terms, the resulting E-tot contains the
> integral (rho *V-coul) and since
> rho is constant (equal to Q/volume), we get the average potential in the
> unit cell (not only the
> interstital, where it is zero anyway) multiplied by the constant rho).
>
> This term is missing when I put a clmsum file with rho=zero, but add a
> "background charge"
> by case.inm, while the resulting potentials are identical for the two
> methods.
>
> However, for a charged bulk system there is still a big problem, because
> V-coul is determined
> only up to a constant and is shifted arbitrarily such that the potential in
> the interstital is zero.
> In "neutral" calculations such a shift does not matter, since it will be
> canceled by the sum of
> eigenvalues, but when adding the constant background it matters.
>
> Thus, this correction term depends on RMT ?
>
> At the moment I'm not sure how I should continue. I think in other codes
> such a correction is
> added, but as mentioned, I guess the correction depends on the arbitrary
> choice of V-zero.
>
>
> Laurence Marks schrieb:
>>
>> 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
>> printedthere). You should do an empty cell test (no electrons) to verify
>> thisand the units of V0, perhaps also looking at the code itself --
>> andremember 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
>> calculati
>
> on 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 no
> t 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>
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>>
>>
>> -- Laurence MarksDepartment of Materials Science and EngineeringMSE Rm
>> 2036 Cook Hall2220 N Campus DriveNorthwestern UniversityEvanston, IL 60208,
>> USATel: (847) 491-3996 Fax: (847) 491-7820email: L-marks at northwestern dot
>> eduWeb: www.numis.northwestern.eduChair, Commission on Electron
>> Crystallography of IUCRwww.numis.northwestern.edu/Electron crystallography
>> is the branch of science that uses electronscattering and imaging to study
>> the structure of matter._______________________________________________Wien
>> mailing
>> listWien at zeus.theochem.tuwien.ac.athttp://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
> --
> -----------------------------------------
> Peter Blaha
> Inst. Materials Chemistry, TU Vienna
> Getreidemarkt 9, A-1060 Vienna, Austria
> Tel: +43-1-5880115671
> Fax: +43-1-5880115698
> email: pblaha at 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.