[gpaw-users] Very anisotropic grid spacings

[Jens Jørgen Mortensen]

On Mon, 2011-02-28 at 09:45 +0100, Jakob Schiøtz wrote:
> I am not really sure, but I think it is because the unit cell is not orthorhombic.  The distance along the three axes is as written in the table, but the distances between the grid lines is different, and anisotropic, as the grid lines are not orthogonal to the axes.  
> 
> I am not sure which of the two distances is important, and I do not understand why the numbers in the error message are larger than in the table, I would expect them to be smaller.  Perhaps somebody else has an opinion.
> 
> Jakob
> 
> On 25 Feb, 2011, at 23:39, Duy Le wrote:
> 
> > Dear all,
> > 
> > I saw that the Sanity check for grid spacings uses the condition
> > max(h_c)/min(h_c) > 1.3. I don't know the purpose of this test. Could
> > someone help me to understand this?
> > 
> > I have a suppercell like this. I want to use (52,76,172) mesh. But it
> > does not pass the Sanity test. I enlarge the limit to 1.7 for letting
> > the job run. not sure if it is okie to do so.
> > 
> > Unit Cell:
> >           Periodic     X           Y           Z      Points  Spacing
> >  --------------------------------------------------------------------
> >  1. axis:    yes    7.806968    0.000000    0.000000    52     0.1501
> >  2. axis:    yes    8.922249    7.726895    0.000000    76     0.1553
> >  3. axis:    yes    0.000000    0.000000   26.329131   172     0.1531
> > 
> > raise ValueError('Very anisotropic grid spacings: %s' % h_c)
> > ValueError: Very anisotropic grid spacings: [ 0.18573318  0.19212781
> > 0.28927234]

Yes, it is the distance between planes of grid points that matter.  In
this example they are 0.18573318, 0.19212781, 0.28927234 Bohr.  We
should probably write these distances in the text output.  Any
suggestions how to do that in a readable and understandable way?

Why is it that you specify 52*76*172 grid points?  If you just specify
h=0.15, you will get a reasonable number of grid points.

See also the h2gpts() function:

https://trac.fysik.dtu.dk/projects/gpaw/browser/trunk/gpaw/utilities/__init__.py#L40

Jens Jørgen

> > 
> > 
> > --------------------------------------------------
> > Duy Le
> > PhD Student
> > Department of Physics
> > University of Central Florida.
> > 
> > "Men don't need hand to do things"
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> 
> --
> Jakob Schiøtz, Ph.D.
> Associate professor (lektor)
> Study leader, M.Sc. in Physics and Nanotechnology
> (kandidatstudieleder, Fysik og Nanoteknologi)
> CINF, Department of Physics
> Technical University of Denmark
> DK-2800 Kongens Lyngby, Denmark
> http://www.cinf.dtu.dk/~schiotz/
> 
> 
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