anti-ferromagnetic Fe

Queries about input and output files, running specific calculations, etc.


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peterklaver
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anti-ferromagnetic Fe

#1 Post by peterklaver » Thu Apr 21, 2005 10:43 am

Hi everyone,

I need to do some calculations on Fe and FeCr dilute alloys in the ferro-magnetic, non-magnetic and anti-ferro magnetic states. The FM and NM states are not a problem, the AFM is. Just setting the initial spins antiFM for a system of mostly Fe doesn't work, VASP converges to a FM solution anyway most of the time. If it finds some other solution it is usually after very difficult convergence with a large difference between the input-output electron density at the final steps. I could try to enforce the moments with some tags in the INCAR file, but I wonder how accurate any results would be. Non-ground states are not too accurately described by DFT, how well would it do for an enforced AFM state for Fe? The difficult convergence and large input-output electron difference for anything other than the FM or NM states make me quite pessimistic about it. How accurate would a 'tortuously imposed' AFM state be? Does anyone know of any good reading on this subject?

greets,
Peter
Last edited by peterklaver on Thu Apr 21, 2005 10:43 am, edited 1 time in total.

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anti-ferromagnetic Fe

#2 Post by admin » Fri Apr 22, 2005 2:18 pm

If the relaxation inevitably tends towards a FM or NM ground state,
you can either
1) fix the total moment of the cell to 0 (NUPDOWN)
to avoid FM solutions or
2) set the directions of the magnetic moments: they can be enforced by constraining the moments:
the tags which have to be set in this case are
LNONCOLLINEAR = .True.
I_CONSTRAINED_M= 1
LAMBDA = r (real number the specify the weight of the penalty terms)
M_CONSTR= m_x m_y m_z (triplet for each ion)

please find additional hints in the VASP online manual,
chapter " Constraining the direction of magnetic moments "
Last edited by admin on Fri Apr 22, 2005 2:18 pm, edited 1 time in total.

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