[Wien] convergence of slab calculations

[Laurence Marks]

So many things!

1. With your RMT's a RKMAX of 5 should be fine. Personaly I do not
believe in using H termination, I consider it flakey. I suspect that
your H RMT is too large.
2. Use a k-mesh which gives you the same density in reciprocal space
as you need for an adequate bulk calculation -- almost certainly you
have way too many.
3. Mixing nodes the way you have is for your machines file can be
disasterous as it can easily lead to more than one mpi task running on
a core (read the mpi release documentation for whatever flavor you are
using). I personally do not know of a system with 3 cores per node,
only 2,4 or 8.
4. I do not believe in fixing atoms. This is "OK" with a bad
minimizer, but not a clever idea with a good one (and PORT is the
best, freely available minimizer written by some of the biggest names
in Minimization in the 80's).

On Tue, Dec 14, 2010 at 9:01 AM, Kakhaber Jandieri
<Kakhaber.Jandieri at physik.uni-marburg.de> wrote:
> Dear Wien2K users,
>
> I am trying to relax GaAs surface with pair of nitrogen impurities.
> For that I construct the supercell with 96 atoms ( Spacegroup: 6_Pm. No
> inversion symmetry).
> In total I have 12 layers with 8 atoms in each.
> First (bottom) layer consists of hydrogen atoms (for passivation).
> Next two layers are fixed.
> In the last (top) layer two As atoms are replaced by nitrogen atoms.
> I generated k-points with following  divisions of the reciprocal lattice
> vectors:
> 10,1,1 (My slab is in x-direction).
> My case.klist file looks as follows:
>         1        10        10         1        20  2.0 -7.0
> 1.5         0 k, div: (  1  1 10)
>         2        10        10         3        20  2.0
>         3        10        10         5        20  2.0
>         4        10        10         7        20  2.0
>         5        10        10         9        20  2.0
> I do the calculations with MPI+k-point parallelization using 20 processors.
> Here is my .machines file:
> granularity:1
> 1:node132:3 node129:1
> 1:node129:2 node124:2
> 1:node124:1 node136:3
> 1:node120:3 node126:1
> 1:node126:2 node134:2
> lapw0: node132:3 node129:3 node124:3 node136:3 node120:3 node126:3 node134:2
>
> My conversion criteria are:
> min -NI -i 10 -s 2  -j 'run_lapw -p -I -i 40 -ec 0.001 -fc 1.0 -cc 0.001'.
>
> Energy tp separate core and valence states is  -6.0 Ry.
> RKmax = 7.0.
> I use the following values of RMT:
> RMT(Ga,As)=2.0
> RMT(N)=1.68
> RMT(H)=1.5
>
> The calculations already took almost the month.
> Six mini cycles are already passed.
> The energy decreases.
> The forces also decrease for all atoms except of those in fixed and
> passivating layers.
> In these layers the forces are extremely large  (around  80)  and
> continue to increase from  cycle to cycle.
> I already don't believe that the supercell will be relaxed at all
> (because of these fixed and passivation layers).
> Could someone give me the advice.
> Is such behavior normal ? if not, what is wrong with my calculations?
>
> Beforehand thankful,
>
> Kakhaber Jandierei.
>
>
>
>
>
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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.