about the fixed magnetic moment

[wenzhouchen]

Hi,
When I do a spin polarized calculation, I set
ENCUT = 320
ISTART = 0; ICHARG = 2
ISMEAR = 0;SIGMA = 0.02
NSW = 60;IBRION = 2
ISPIN = 2
LORBIT = 12
MAGMOM = 2*4.5 2*0
ISIF = 3
POTIM = 0.5
EDIFF = 1E-8;EDIFFG = 1E-8
PREC = Accurate
however, when I do another calculation,only the change in the MAGMOM(do not specify the MAGMOM), I have the same result
magnetization (x)

# of ion s p d tot
----------------------------------------
1 0.026 0.020 2.591 2.637
2 0.027 0.019 2.597 2.644
3 -0.001 -0.102 0.007 -0.096
4 -0.001 -0.102 0.007 -0.096
------------------------------------------------
tot 0.052 -0.166 5.201 5.088

The same similar result I get when I do a single point calculation.
(1) I have set the Magmom to 4.5, why I get the magmom 2.637 and 2.644?
(2) Can I do a fixed magnetic moment calculation?
Thanks for your help.

[forsdan]

(1) MAGMOM sets the initial guess for the magnetic moments. It is NOT the scf-solution. The magnetic moments you see is the scf-solution (within the RWIGS radii).

(Please also note that when you don't specify MAGMOM it will default to 1 for each atom, i.e. MAGMOM = 4*1 in your case. )

(2) You can fix the magnetization for the entire cell by using NUPDOWN, but you cannot fix magnetic moments on specific atoms.

Cheers,
/Dan
<span class='smallblacktext'>[ Edited Tue Sep 20 2011, 12:20PM ]</span>