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

[Paolo Giannozzi]

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

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Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
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