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["matthieu verstraete" <matthieu.jean.verstraete@gmail.com>]

Hello Petr and Ganesh,

indeed, the standard relaxation modes in abinit do not allow you to do what you describe if the primitive vector you want to relax is not perpendicular to the other two. This is because the strain tensor is applied in cartesian coordinates, and fixing the first 2 vectors effectively imposes strain = identity unless alpha=beta=90deg. It would be very interesting to hear what you did Petr - would you mind elaborating (even if it does not solve Ganesh's problem)? It would be even better if you could commit a new optcell to the abinit code! I have given a bit of thought to how to go about this relaxation, but it doesn't seem too obvious.
Perhaps translating the strain to reduced coordinates and then setting certain columns of the strain to 1 0 0  or  0 1 0...

cheers

Matthieu

On Sat, Dec 20, 2008 at 11:15 PM, Petr <sestak@kn.vutbr.cz> wrote:

Hi,

I had the same problem as you. I have been doing some relaxation on the
monoclinic structure and I couldn't use the standard relaxation procedure. I
solved this problem by writing an own relaxation procedure which is relaxing
parameters RPRIM according to the computed elastic tensor. If you can be more
specific in detail I might by able to tell you if the same procedure can help
you.

Best regards

Ing. Peter Sestak
Institute of Physical Engineering
Faculty of Mechanical Engineering
Brno University of Technology

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Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF) 
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