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

[Rasmus Karlsson]

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.

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 
>
> 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
>>
>
>

-- 
Rasmus Karlsson, PhD student
Applied Electrochemistry
School of Chemical Science and Engineering
KTH Royal Institute of Technology
SE-100 44 Stockholm
Sweden