[Wien] Bad formation energies for the charged vacancies

Thu Feb 25 00:13:23 CET 2010

Thank you for the replies. I thought that such a correction was
already done in Wien2k. I should have noticed the warning in case.scf0
file:
:WARN  :        CHARGED CELL with  -1.000
        an energy correction like C Q**2/(L eps) is not included
(PRB51,4014; PRB73,35215)

I'm not sure if I understand it correctly:

1. The value of V_0 is written in case.scf0 file and is marked as
VCOUL-ZERO for each atom. So, should one take the sum of VCOUL-ZERO of
all the atoms?

2. As V_0  is arbitrarily defined, one should make some reference
calculation  and use the potential difference V_0(q)-V_0_ref, right?.

So, is the problem that the "shift" which corresponds to zero is
different for the different charge states and we cannot just take the
value of V_0 from the neutral cell as the reference? Or, will the
calculation for an empty cell (0 electrons) be such a reference?

with kind regards,
Yurko

On 24 February 2010 22:58, Laurence Marks <L-marks at northwestern.edu> wrote:
> 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>
>> Wien at zeus.theochem.tuwien.ac.at>
>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien>
>>>
>>>
>>> -- 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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>> Wien mailing list
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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.
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>

-- 
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