[gpaw-users] Mn2O3 lattice parameter using StrainFilter

[Jens Jørgen Mortensen]

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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