[gpaw-users] Mn2O3 lattice parameter using StrainFilter

[Jens Jørgen Mortensen]

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.

Jens Jørgen

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

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