[Pw_forum] Pw.x : relaxation in crystall coordinates?

[Alexander Shaposhnikov]

Hi,
this idea comes to in the first place. So, i made some distortion
in crystall coordinates "by hand". To my great surprise, the total force
still was zero! I made a run with nosym=.TRUE., still no effect.
(And in alat units total force is not that small, by the way.)

I use the latest cvs version. No changes wrt 3.0. 

Regards,
Alex

On Thu, 2005-12-15 at 09:02 -0500, Axel Kohlmeyer wrote:
> On Thu, 15 Dec 2005, Alexander Shaposhnikov wrote:
> 
> AS> Hello,
> 
> hi!
> 
> AS> is it possible to make structural relaxation with input coordinates
> AS> in "crystall" units? Total force always calculated = 0 and no
> 
> yes. of course.
> 
> AS> relaxation is done. The same system input in "alat" units (coordinates
> AS> taken from pw.x output) have non-zero total force.
> 
> this is because of the limited numerical accuracy in the output.
> seems like in your starting configuration, the forces cancel exactly
> due to symmetry. just break the symmetry for 1-2 atoms in the input
> by adding a small displacement and you should see a similar behavior
> as when using alat based coordinates.
> 
> axel.
> 
> AS> 
> AS> Thanks.
> AS> 
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