Sorry
I believe that I have found the solution. I use the next constr.f:
This file is part of the SIESTA package.
!
! Copyright (c) Fundacion General Universidad Autonoma de Madrid:
! E.Artacho, J.Gale, A.Garcia, J.Junquera, P.Ordejon, D.Sanchez-Portal
! and J.M.Soler, 1996-2006.
!
! Use of this software constitutes agreement with the full conditions
! given in the SIESTA license, as signed by all legitimate users.
!
c $Id: constr.f,v 1.6 2003/06/23 09:46:16 ordejon Exp $
subroutine constr( cell, na, isa, amass, xa, stress, fa, ntcon )
c *****************************************************************
c User-written routine to implement specific geometric constraints,
c by orthogonalizing the forces and stress to undesired changes.
c Arguments:
c real*8 cell(3,3) : input lattice vectors (Bohr)
c integer na : input number of atoms
c integer isa(na) : input species indexes
c real*8 amass(na) : input atomic masses
c real*8 xa(3,na) : input atomic cartesian coordinates (Bohr)
c real*8 stress( 3,3) : input/output stress tensor (Ry/Bohr**3)
c real*8 fa(3,na) : input/output atomic forces (Ry/Bohr)
c integer ntcon : total number of positions constr. imposed
c *****************************************************************
implicit none
integer na, isa(na), ntcon
double precision amass(na), cell(3,3), fa(3,na),
. stress(3,3), xa(3,na)
c Write here your problem-specific code.
cell(1,2)=0.0
cell(1,3)=0.0
cell(2,1)=0.0
cell(2,3)=0.0
cell(3,1)=0.0
cell(3,2)=0.0
return
end
Anyway, thanks
> Hi all
> I am trying to optimize a crystal with some constrains. I want only
> optimize cell sides, but no cell angles. For this, I add the next block
> label:
> %block GeometryConstraints
> stress 2 3 4 6 7 8
> %endblock GeometryConstraints
>
> I thought that stress 1, 3 and 9 are correlated with axis a, b and c
> respectively (and unit cell vectors a11, a22 and a33). The remaining
> stress are corresponding to cell angles. I am sure that a11, a22, a33 are
> the cell side.
> Of this way, a12, a21, a22, a23, a32 and a33 positions of out cell are
> constants during the optimization.
> Does someone know the transformation matrix that SIESTA uses?
>
> I hope that you can understand me without problem
>
> Thank in advance
>
> Gregorio
>
