Hi,
  
  I think there a small confusion !! If I well understood the primary  mail :
  
  > %block GeometryConstraints
  > position 27 0.1  0.0  0.0
  > position 27 0.0  0.0  0.1
  > %endblock GeometryConstraints
  
  1.0 and 0.0 indicate logical variables !!! freeze or not the corresponding 
coordinate (x or z). !!!
  
  so, after cheking the subroutines consrt.f and fixed.f, I think  freezing a 
one coordinate of a particular atom should be performed as  follow:
  
  %block GeometryConstraints
    routine constr
  %endblock GeometryConstraints
  
  this will direct the program to the subroutine constr.f
  
  Finally one has to write a small procedure in constr.f where the forces  
related to the frozen components (of the target atom) have to be set to  0.0 :
  
  fx=0.0
  fz=0.0
  
  hope this will help !!
  
  Cheers,
  Imad
  
  
  

Marcos Verissimo Alves <[EMAIL PROTECTED]> a écrit :  Seems so. But, if you are 
really unsure and want to clear any doubts, you
can test this kind of block on a smaller system, or use your 55 atom
system with a low cutoff, SZ basis set and a finite number of scf/cg steps
(3 for each should do the job), just to speed up things and see what
happens. Then check the .ANI file using molden, or by yourself...

Cheers,

Marcos

> Dear siesta users,
> I have a structure of 55 atoms, numbered from 1 to 55.
> I  need to freeze the x and z components of atom 27.
> How to do this? Is it right like this?
>
> %block GeometryConstraints
> position 27 0.1  0.0  0.0
> position 27 0.0  0.0  0.1
> %endblock GeometryConstraints
>
> Akli,
> Thanks
>
>
>
>
>
>
>
> ___________________________________________________________________________
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-- 
Dr. Marcos Verissimo Alves
Post-Doctoral Fellow
Condensed Matter and Statistical Physics Sector
International Centre for Theoretical Physics
Trieste, Italy

--------

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