[gpaw-users] GPAW PW crashes if ecut is too high

[Michael Walter]

2013/9/5 Jens Jørgen Mortensen <jensj at fysik.dtu.dk>

> Den 02-09-2013 20:21, Rasmus Karlsson skrev:
>
>> Hi Marcin!
>>
>> I see... Do you know of any way to get around this problem that does not
>> require me to set really low grid spacings (I had to go to h=0.10 Å, which
>> will probably be quite time consuming)? The problem is of course that I
>> want the ability to optimize cell size and atomic positions at the same
>> time, which is hard to manage without UnitCellFilter. I could of course
>> just scale the volume of the cell to a couple of point and fit an EOS, but
>> for this system I'm not sure the cell angles will stay exactly the same
>> after relaxation. I guess the problem lies in how GPAW creates its grids in
>> these kinds of cells, so it's not a matter of using some other ASE
>> optimizer instead?
>>
>> In any case, if the only solution is running with h=0.10 Å, that's what
>> I'll do.
>>
>
> The best solution right now is to choose the unit cell vectors so that the
> angles between them are closer to 90 degrees - that would cure the problem
> (choose the third axis as a1+a3 or something like that).
>

Please note, that there is a helper function to do that automatically in
ase now:
https://trac.fysik.dtu.dk/projects/ase/browser/trunk/ase/utils/geometry.py#L504
https://trac.fysik.dtu.dk/projects/ase/browser/trunk/ase/utils/geometry.py#L474

example use:

from ase.utils.geometry import minimize_tilt

atoms = ...

# reduce angles as much as possible
minimize_tilt(atoms)


Michael




>
> Ideally, GPAW should be able to handle such strange cells, but I will not
> have time to fix it right now.  Let me know If anyone wants to dig into the
> PW code and help fix the problem.
>
> Jens Jørgen
>
>
>
>> Thanks!
>>
>> Rasmus
>>
>> On 09/02/2013 12:58 AM, Marcin Dulak wrote:
>>
>>> Hi,
>>>
>>> On 09/01/2013 12:26 AM, Rasmus Karlsson wrote:
>>>
>>>> Hi!
>>>> I just tried starting a PW calculation for relaxation of a unit cell of
>>>> CmC2_1 space group. However, GPAW immediately crashes with
>>>> ../gpaw/wavefunctions/pw.py", line 37, in __init__
>>>>     assert ((gd.h_cv**2).sum(1) <= 0.5 * pi**2 / ecut).all()
>>>>
>>> this is a known problem with skewed cells:
>>> https://listserv.fysik.dtu.dk/**pipermail/gpaw-developers/**
>>> 2012-May/002870.html<https://listserv.fysik.dtu.dk/pipermail/gpaw-developers/2012-May/002870.html>
>>> You need to set h manually (in addition to PW) to a very small value.
>>>
>>> Best regards,
>>>
>>> Marcin
>>>
>>>>
>>>> If running through with pdb, (gd.h_cv**2).sum(1) is
>>>> array([ 0.05550866,  0.25919729,  0.25919729])
>>>> and
>>>> 0.5*pi**2/ecut is
>>>> 0.22380475860123122
>>>> Obviously, the second and third item in the array is too big. Reducing
>>>> the cutoff from 600 eV to 500 eV makes it work. This is somewhat strange.
>>>>
>>>> gd.h_cv is
>>>> array([[  2.35602765e-01,   0.00000000e+00,   0.00000000e+00],
>>>>        [  3.11742550e-17,   5.09114220e-01,   0.00000000e+00],
>>>>        [  3.11742550e-17,  -4.50356897e-01, 2.37436210e-01]])
>>>>
>>>> Can anyone comment on what is going on? Am I doing something wrong, or
>>>> is GPAW behaving strangely?
>>>>
>>>> The calculation was run with v. 0.9.1.10258
>>>>
>>>> Thanks,
>>>> Rasmus
>>>>
>>>>
>>>
>>>
>>
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-- 
------------------------------------------
PD Dr Michael Walter
Address: Freiburger Materialforschungszentrum
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