How to make ferro, feri and antiferro magnetic structure for QE

Question

I have below &SYSTME information from my input file

      &CONTROL
      calculation = 'scf'
      etot_conv_thr =   1.0000000000d-04
      forc_conv_thr =   1.0000000000d-04
      outdir = './tmp/'
      prefix = 'pwscf'
      pseudo_dir = './'
      tprnfor = .true.
      tstress = .true.
      verbosity = 'high'
    /
    &SYSTEM
      degauss =   1.4699723600d-02
      ecutrho =   3.6000000000d+02
      ecutwfc =   4.5000000000d+01
      ibrav = 0
      nat = 12
      nosym = .false.
      ntyp = 2
      occupations = 'smearing'
      smearing = 'cold'
    /
    &ELECTRONS
      conv_thr =   1.0000000000d-09
      electron_maxstep = 100
      mixing_beta =   3.0000000000d-01
    /
    ATOMIC_SPECIES
    Ta       ta_pbe_v1.4.uspp.F.UPF
    Ni       ni_pbe_v1.4.uspp.F.UPF
    ATOMIC_POSITIONS crystal
   Ta            0.0000000000       0.0000000000       0.2500000000 
   Ta            0.0000000000       0.0000000000       0.7500000000 
   Ta            0.5000000000       0.5000000000       0.7500000000 
   Ta            0.5000000000       0.5000000000       0.2500000000 
    Ni           0.1677000000       0.6677000000       0.0000000000 
    Ni           0.3323000000       0.1677000000       0.0000000000 
    Ni           0.8323000000       0.3323000000       0.0000000000 
    Ni           0.6677000000       0.8323000000       0.0000000000 
    Ni           0.1677000000       0.3323000000       0.5000000000 
    Ni           0.6677000000       0.1677000000       0.5000000000 
    Ni           0.8323000000       0.6677000000       0.5000000000 
    Ni           0.3323000000       0.8323000000       0.5000000000 
    K_POINTS automatic
    7 7 8 0 0 0
    CELL_PARAMETERS angstrom
          4.9910000000       0.0000000000       0.0000000000
          0.0000000000       4.9910000000       0.0000000000
          0.0000000000       0.0000000000       4.2470000000

How can I make ferromagnetic, anti-ferromagnetic, and ferrimagnetic structures from it?

Answer 1

Since the question concerns only magnetic order, I am going to address only that, leaving out details about smearing and other parameters.

Let's take a simple A-type magnetic system from this illustration.

Note that there are primarily two types of magnetism: Intra-layer and inter-layer. I would advise the following procedure for creating your input file:

1. Determine what atoms in your system are magnetic - Is it the Ni, Ta etc..
2. Determine what kind of spin arrangement you require - pay attention to both intra-layer and inter-layer channels.

As an example, let me work with the system in your question. Let's assume the nickel atoms are magnetic. You can clearly notice that 4 nickel atoms are in the same plane, and they are separated by half a lattice constant along 'z'. I can outline some ideas so that you get the general gist.

a) A type antiferromagnet:

Ni1           0.1677000000       0.6677000000       0.0000000000 
Ni1           0.3323000000       0.1677000000       0.0000000000 
Ni1           0.8323000000       0.3323000000       0.0000000000 
Ni1          0.6677000000       0.8323000000       0.0000000000 
Ni2           0.1677000000       0.3323000000       0.5000000000 
Ni2           0.6677000000       0.1677000000       0.5000000000 
Ni2           0.8323000000       0.6677000000       0.5000000000 
Ni2           0.3323000000       0.8323000000       0.5000000000 

You would set starting_magnetization of Ni1 as 1 and starting_magnetization of Ni2 as -1.

b) C-type antiferromagnet:

Ni1           0.1677000000       0.6677000000       0.0000000000 
Ni2           0.3323000000       0.1677000000       0.0000000000 
Ni1           0.8323000000       0.3323000000       0.0000000000 
Ni2          0.6677000000       0.8323000000       0.0000000000 
Ni1           0.1677000000       0.3323000000       0.5000000000 
Ni2           0.6677000000       0.1677000000       0.5000000000 
Ni1           0.8323000000       0.6677000000       0.5000000000 
Ni2           0.3323000000       0.8323000000       0.5000000000 

You would set starting_magnetization of Ni1 as 1 and starting_magnetization of Ni2 as -1.

I hope you get the idea. For ferrimagnets, you would set the magnetization values so that the net value (whether intra or inter, depending on your system) is non-zero. Also keep in mind that for some systems the magnetic ordering of spins is in a specific direction - for example NiO. In these cases, I would advise you to thoroughly research the arrangement of spins before formulating your input file.