[gpaw-users] Mn2O3 lattice parameter using StrainFilter

[Teemu Parviainen]

Hi and thank you!
At the moment I am unable to test the new code but I will do it early next
week.

-Teemu


On 17 October 2013 09:49, Jens Jørgen Mortensen <jensj at fysik.dtu.dk> wrote:

>  Den 17-10-2013 06:38, Jens Jørgen Mortensen skrev:
>
> Den 07-10-2013 11:54, Jens Jørgen Mortensen skrev:
>
> Den 03-10-2013 13:02, Teemu Parviainen skrev:
>
>  Dear GPAW users
>
> I'm trying to resolve the lattice parameter of cubic Mn2O3 bulk structure
> with StrainFilter class (GPAW version 0.9.1.rev10611 and ASE 3.7.1).
> However, the method does not yield any good results as the lattice
> immediately starts to shrink and deform. Basically here are the steps I try
> to do:
>
> 1. I generate the structure using Crystal-package and relax it. The energy
> of the final structure is -636.18 eV with total force of 0.0262
> 2. Load up the output file to the Strainfilter-script and try to optimize
> the lattice parameter
>
> However step 2 fails. The calculation converges fine but the total force
> of the structure is ridiculously large which I find very weird. The .log
> file looks basically like this:
>
>     -636.179147    6725.2886
>     -630.665535    6649.4279
>     -618.996444    6554.3936
>     -599.934434    6439.1574
>
>  Calculator parameters in both scripts are the same:
>
>  calc = GPAW(
>                 mode=PW(900),
>                 nbands=-40,
>                 xc='PBE',
>                 maxiter=240,
>                 width=0.2,
>                 spinpol= True,
>                 mixer=MixerSum(0.02, 2, 50),
>                 kpts=(1,1,1),
>                 txt=name + '.txt',
>                 setups={'Mn': 'paw:d,3.9'}  #Hubbard U for increasing band
> gap
>         )
>
> The same method works fine for example for Cu2O and CuO bulk structures,
> which we have calculated recently.
>
> Other things I have tried:
>     -Perform the calculation without using spins
>     -Generate the structure within StrainFilter-script and not relax it
> first
>     -Use different values of plane-wave cut-off energy
>     -Use different values of initial lattice constant
>
> All these have yielded same kind of results.
>
> Attached are the relevant scripts and output files. Any help would be
> kindly accepted.
>
>
> The StrinFilter multiplies the 6 components of the stress by the volume
> and then converts those numbers to forces acting on two atoms so that we
> can use our normal optimization algorithms which can only handle atoms.
>
> Since your volume is quite high, the "atomic" forces will be high too.
> Maybe that is confusing the algorithm - I'll take a look.
>
>
> Looks like a bug in GPAW's stress code :-(
>
> I think the problem is only there for gamma-point only calculations (like
> yours), so you could try kpts=(2,2,2) until I have solved the problem.
>
>
> I think I have fixed it.  Could you give the latest version a try?
>
> Jens Jørgen
>
>
>
> Jens Jørgen
>
>
> Jens Jørgen
>
>  -Teemu Parviainen
> PhD student
> University of Jyväskylä, Nanoscience Center, Finland
>
>
>
>
>
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