[Wien] segmentation fault in spaghetti
Gerhard Fecher
fecher at uni-mainz.de
Mon Jan 5 20:18:43 CET 2009
If the symmetry is the same then the k-list should be the same, as a point at x y z in fractional coordinates should still be at x y z.
However, if you increase the Wigner Seitz cell by increasing the lattice parameter you shrink the Brillouin zone to become
incredibly small and finally reduces to the Gamma point and a band structure makes not real sense because of the backfolding effect.
If you like to check for bandgaps, you may inspect the regular output files of the scf cycle, there is no need to draw a bandstructure.
Ciao
Gerhard
====================================
Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
________________________________________
Von: wien-bounces at zeus.theochem.tuwien.ac.at [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von Ludwig, Christian [ludwigc at uni-mainz.de]
Gesendet: Montag, 5. Januar 2009 16:26
An: A Mailing list for WIEN2k users
Betreff: [Wien] segmentation fault in spaghetti
This is still about my calculation with 128 atoms. I could produce a DOS and it looks sensible but I have a problem with getting the bandstructure
I used an xcrysden.klist file and x lapw1 -band -p was fine. After inserting the Fermi energy I started spaghetti (via w2web-interface) and got:
Segmentation fault
0.738u 0.447s 0:01.18 99.1% 0+0k 0+0io 0pf+0w
error: command /usr/local/wien2k/spaghetti spaghetti.def failed
I tried removing the case.irrep (found something about that in the mailing list), but it did not have any effect. Now I was thinking: Can I use a klist file which was created for one unit cell for a supercell? When I look at the k-points of the supercell with xcrysden, I see no difference to the unit cell. What else could it be? All the error files are empty.
Happy new year!
Christian
________________________________________
Von: wien-bounces at zeus.theochem.tuwien.ac.at [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von Peter Blaha [pblaha at theochem.tuwien.ac.at]
Gesendet: Donnerstag, 18. Dezember 2008 12:03
An: A Mailing list for WIEN2k users
Betreff: Re: [Wien] runtime for lapw2 -qtl -p
For your original cell (with 16 atoms) you do NOT need a 10x10x10 mesh, because this
cell is much larger than fcc-Cu (16 times larger, thus your mesh can be
16 times smaller)!
In addition it is a semiconductor, thus you do NOT have any effects due to partially
occupied bands (Fermi surface effects), which usually also means reducing the mesh by an
order of magnitude.
In essence: I'm pretty sure that your scf calculation can be done with A SINGLE k-point
(maybe use 2-4 if you have more processors anyway), while for a DOS you should use a bit
larger mesh (use something like 16 k-points if you have 16 processors), otherwise you
get a very "spiky" DOS (or no DOS for a single k-point, because the tetrahedron
integration does not capture the set of delta-functions coming from a single k-point).
Ludwig, Christian schrieb:
> My supercell is only 2x2x2, the complicated unit cells makes for 128 atoms total. So as I understand it, my 108 k-point are effectively worth 864 k-points, which is not terribly much. And I am dealing with a semiconductor, no idea how that influences a reasonable number of k-points.
>
> Thanks for your comments.
> Cheers,
> Christian
> ________________________________________
> Von: wien-bounces at zeus.theochem.tuwien.ac.at [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von Peter Blaha [pblaha at theochem.tuwien.ac.at]
> Gesendet: Donnerstag, 18. Dezember 2008 11:17
> An: A Mailing list for WIEN2k users
> Betreff: Re: [Wien] runtime for lapw2 -qtl -p
>
> Yes, x lapw2 -qtl -p runs actually on only one processor. It also does a lot of
> I/O, thus it is for bigger cases quite slow (but you do it only once and it blocks
> only one processor).
>
> On the other hand: why are you using for a 128 atom supercell 108 k-points ?
>
> If you do fcc Cu a "poor" k-mesh is 10x10x10, a good one 20x20x20.
> A 5x5x5 supercell of Cu (125 atoms/cell) would thus need a 2x2x2 (or 4x4x4)
> mesh, which even without symmetry (but plus inversion) would lead to only
> "a few" k-points in the BZ.
>
> If you have an insulator, this k-mesh can be reduced by another order of magnitude.
>
> Use a mesh which is in a reasonable range and optimally compatible with your 16
> processors.
>
>
> Ludwig, Christian schrieb:
>> Hello,
>>
>> I am calculating a 128 atom supercell with a random distribution of a constituent, so no symmetry operations. The SCF converged in 75 hours (22 iterations, 108 k-points, 16 procs) and now I am running lapw2 -qtl -p to get the DOS. Since this is not parallel it takes an awful lot of time. Over 50 hours and still running. Now I cannot help but wonder: Is it normal, that this part takes as long as the total SCF convergence or is there something wrong?
>>
>> Kind regards,
>> Christian
>> _______________________________________________
>> Wien mailing list
>> Wien at zeus.theochem.tuwien.ac.at
>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
> --
>
> P.Blaha
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-15671 FAX: +43-1-58801-15698
> Email: blaha at theochem.tuwien.ac.at WWW: http://info.tuwien.ac.at/theochem/
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P.Blaha
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Phone: +43-1-58801-15671 FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at WWW: http://info.tuwien.ac.at/theochem/
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