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

[Axel Kohlmeyer]

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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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
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