[gpaw-users] Mn2O3 lattice parameter using StrainFilter

[Teemu Parviainen]

Hi all,
The code seems to work now, at least the forces and energies behave
reasonably. Also, indeed, increasing the number of k-points helped so the
origin of the problem was there. Thank you very much Jens!

-Teemu Parviainen


On 17 October 2013 13:18, Teemu Parviainen <
teemu.t.parviainen at student.jyu.fi> wrote:

> 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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