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

[Alexander Shaposhnikov]

Silly me:) Thank you!


On Fri, 2005-12-16 at 13:07 +0100, Paolo Giannozzi wrote:
> On Friday 16 December 2005 12:17, Alexander Shaposhnikov wrote:
> 
> > ATOMIC_POSITIONS {crystall}
> 
> "crystal", actually (but this is not relevant, provided the string 
> matches "crystal).
> 
> >     Zr     0.750000000    0.250000000    0.250000000    0  0  0
> >     Zr     0.250000000    0.750000000    0.750000000    0  0  0
> >     O      0.250000000    0.250000000    0.454600000    0  0  0
> >     O      0.750000000    0.750000000    0.545400000    0  0  0
> >     O      0.250000000    0.250000000    0.954600000    0  0  0
> >     O      0.750000000    0.750000000    0.045400000    0  0  0
> 
> > [...] In the case of {crystall} coordinates, total force is always zero.
> 
> of course it is: you are setting it to zero. From INPUT_PW:
> 
>   X  x y z   {if_pos(1) if_pos(2) if_pos(3)}
> 
> where :
> 
>   X           Character: label of the atom as specified in ATOMIC_SPECIES
>   x, y, z     Real: atomic positions
>   if_pos:     Integer: component i of the force for this atom is multiplied
>               by if_pos(i), which must be 0 or 1. Used to keep selected atoms
>               and/or selected components fixed in neb, smd, MD dynamics or
>               structural optimization run
> 
> If you set these to zero, you set to zero the forces
> 
> Paolo
>