[Pw_forum] Questions about ionic & cell relaxation.
giannozz at nest.sns.it
Sun Jan 20 17:07:51 CET 2008
On Jan 19, 2008, at 19:13 , Hongbin Zhang wrote:
> 1) if the symmetry will be kept, then how can I break the symmetry if
try with a hammer :-)
Seriously: move one or a few atoms away from their symmetric positions
> 2) I think there is a Keyword "nosym" in the namelist "&SYSTEM", is it
> somehow related to structure relaxation?
what the "nosym" option (a very misleading name in my opinion) does
is explained in detail and exactly in the INPUT_PW file. Do not use it
unless you understand it.
> 3) In "ATOMIC_POSITIONS" catalog, it's possible to set "if_pos" terms,
> which will make forces along some directions to be zero. How should I
> combine these options with "nosym" option?
these two options do not interact at all
> 1) optimization with mirror symmetry along z direction
> 2) optimization without mirror symmetry along z direction
> So if the original supercell have the z-mirror symmetry, how to
> break it
> if relaxation will keep all symmetry pwscf find (nicola)?
move just one atom from (x,y,z) to (x,y,z+dz), with dz > 10^(-5)
Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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