Thanks a lot Marcos, Karim
Karim, I'd say that the basis set deosn't play as much an influence on the final symmetry of the unit cell (at least in Siesta) as much as a fine real-space mesh. However, if you know which symmetrization operations on forces and stresses maintain the symmetry of a cell, then you can implement them in the file constraints.f, re-compile siesta and use %block GeometryConstraints routine constr %endblock GeometryConstraints in your fdf file.Of course, you are advised to check the manual for the exact syntax of this block, as well as the programming of the constraints in this file :) Marcos On Sun, Jan 30, 2011 at 12:03 PM, karim rezouali <rezoual...@yahoo.fr> wrote: Dear Users, Is there a way to relaxe both atomic positions and cell vectors ( variable cell optimization) of a given system without changing the shape of the supercell (preserving the symmetry) by a judicious choice of PAO basis sets? Karim