MAGMOM-tag

Default

NIONS*1

Specifies the initial magnetic moment for each atom, if and only if ICHARGis equal 2, or if the CHGCAR file contains no magnetisation density (ICHARG=1). If one is searching for a spin polarised (magnetic or antiferromagnetic) solution, it is usually safest to start from larger local magnetic moments, and in some cases, the default values might not be sufficiently big. A save default is usually the experimental magnetic moment multiplied by 1.2 or 1.5. It is important to emphasis that the MAGMOM tag is used only, if the CHGCAR file holds no information on the magnetisation density, and if the initial charge density is not calculated from the wavefunctions supplied in the WAVECAR file. This means that the MAGMOM tag is usefull for two kind of calculations

• Calculations starting from scratch with no WAVECAR and CHGCAR file.
• Calculations starting from a non magnetic WAVECAR and CHGCAR file ( ICHARG= 1). Often such calculations converge more reliably to the desired magnetic configuration than calculations of the first kind. Hence, if you have problems to converge to a desired magnetic solution, try to calculate first the non magnetic groundstate, and continue from the generated WAVECAR and CHGCAR file. For the continuation job, you need to set

  
   ISPIN=2
   ICHARG=1
  

  in the INCAR file.

Starting from VASP.4.4.4, VASP also determines, whether the magnetic moments supplied in the MAGMOM line break the symmetry. If they do, the corresponding symmetry operations are removed and not applied during the symmetrization of charges and forces. This means that antiferromagnetic calculations can be performed by specifying anti-parallel magnetic moments for the atoms in the cell

 MAGMOM = 1 -1

As an example considere AF bcc Cr with the POSCAR file:

Cr: AF
 2.80000
  1.00000   .00000   .00000
   .00000  1.00000   .00000
   .00000   .00000  1.00000
  1 1
Kartesisch
   .00000   .00000   .00000
   .50000   .50000   .50000

With the MAGMOM line specified above, VASP should converge to the proper groundstate. In this example, the total net magnetisation is matter of factly zero, but it is possible to determine the local magnetic moments by using the RWIGS or LORBIT tags (see sections 6.33 6.32).