[Wien] About antiferromagnetism calculation

[Antoine Villesuzanne]

I have sometimes encoutered this type of problem : starting from antiparallel spins and using the "runafm" script may lead to a non-magnetic or to a ferromagnetic solution, even though the ground state turns out to be the antiferromagnetic one, at last (from the Wien calculations). 
For example, this was the case of TeCuO3 (Chem. Mater. 17, 4350, 2005). 

The trick is then to : 
- check the evolution of the magnetic moments along the iterations, 
- when close to the expected values, stop the "runafm" calculation,
- restart with "runsp" until convergence.

or, run the AFM calculation with runsp only (i.e. with spins flipped but without clmcopy)

Antoine Villesuzanne
ICMCB-CNRS
87, Av. Dr. A. Schweitzer
33608 Pessac Cedex
Tél. 33 (0) 540008459
Fax 33 (0) 540008373
  ----- Original Message ----- 
  From: Eric Sun 
  To: wien at zeus.theochem.tuwien.ac.at 
  Sent: Wednesday, August 31, 2005 6:12 PM
  Subject: [Wien] About antiferromagnetism calculation


  Dear WIEN2k users,

  I'm trying to do some antiferromagnetism calculations.
  I read the FAQ in the following page
  http://www.wien2k.at/reg_user/faq/afm.html
  I realize that an important step in the AFM calculations 
  is to manually flip one of the spins of two adjacent
  magnetic atoms. My simple question is that
  if this step is to avoid the so-called "local minimum"
  in the variational procedure. I mean, if we just leave 
  the two spins parallel, will the variational procedure
  always stop at some ferromagnetic state? Or, 
  is it possible that, even if the spins are initially
  antiparallel, they may ocassionally drop in 
  the ferromagnetic "local minimum" in the variational
  procedure?

  Thanks for your kindly reply.
  Eric



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