[Wien] SECLR4 error in large supercells / high number of k points

[Laurence Marks]

:NEC 1e-3 away is LARGE, not small. How big is the second term (which
is a multiplying scalar) -- it should be at most different from one in
the last digit. However, this may not be the issue.

I would suggest tailoring your linearization energies a bit. There is
a unexplained (to me anyway) "ghost force" that can occur sometimes,
and there might be a resonance condition (a little like what was
described in the emails you referenced earlier) which has not been
found as yet. It may be that if you change the linearization energies
a bit you will move away from the condition that is giving you the
problem to a "good" region.

On Thu, Apr 1, 2010 at 7:10 AM, Kurt Lejaeghere
<kurt.lejaeghere at ugent.be> wrote:
> I have tried out all of your ideas:
>
>> Assuming that there is nothing wrong with your LAPACK (sometimes there
>> is), normally I run across this type of problem when something has
>> gone wrong with the potential due to a bad initial density (from
>> dstart)
>
> The problem mostly occurs only after a few iterations and at a charge
> distance :DIS that is already reasonably small ( < 0,01). Sometimes the
> calculations work without a glitch, but very small changes (e.g. a change in
> the internal positions) can lead to a SECLR4 error.
>
>> a ghost-band that is not quite big enough to crash lapw2 (but
>> gives a warning)
>
> Sometimes warnings occur in this series of calculations, because of a small
> QTL-B error (2 to 3). However not all cases with a warning give rise to a
> SECLR4 error and not all cases with a SECLR4 error cause such a warning.
>
>> -- In case.scf0 -- do the fits (at the end) and the VZER terms look
>> reasonable compared to what you have for a smaller case?
>
> As far as I can see they do. :FIT is constantly of the order of magnitude of
> 1E-2 or 1E-3 and the :VZER are, both for a problematic and a correct case,
> either simultaneously zero or of the same order of magnitude.
>
>> -- If it ran for a cycle or so, look in case.scfm (also in case.scf)
>> and see if there are very large differences in the QMT's, indicating
>> that you are far from a solution.
>
> If you mean the values of :BIG, they are smaller than 1E-1.
>
>> -- Similarly look in case.outputm at the core integrals -- they should
>> be close to an integer. If not you may need to change the lower energy
>> limit because you have semi-core states which should be in the valence
>> band but are in the core.
>
> All core integrals are at the most 1E-6 away from an integer value.
>
>> -- Similarly look in case.scf(m) at the :NEC terms to see if you are
>> losing electrons.
>
> All terms are at the most 1E-3 away from an integer value, so this should be
> good enough.
>
> Nothing from this list seems to solve the problem. As far as I can see there
> is nothing wrong with the calculations, since similar cells with less (but
> still enough) k points don't cause SECLR4 errors.
>
> With kind regards
>
> Kurt Lejaeghere
> Ghent University
>
>
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>



-- 
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.