[Wien] Bad formation energies for the charged vacancies

[Peter Blaha]

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

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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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