[gpaw-users] Mn2O3 lattice parameter using StrainFilter

[Teemu Parviainen]

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.

-Teemu Parviainen
PhD student
University of Jyväskylä, Nanoscience Center, Finland
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