How to model an anti-ferromagnetic crystal in quantum ESPRESSO properly?

Question

I'm fairly new to DFT. I would like to plot the DOS and band structure of Cobalt Oxide (CoO). But since CoO is anti ferro magnetic, how would I approach the problem? would I create an input file wherein I should assign starting magentization to spins as follows:

by using names like Co1 and Co2 in the Atomic species name card. Or would the act of putting nspin = 2, along with a starting magnetisation for all cobalt atoms suffice? Maybe someone who is experience could shed some light on how to properly model an anti-ferro magentic system.

Thank you.

Answer 1

• The key point is the setting of starting_magnetization. You can find an explanation on the pw.x input description page.

• Here I give you an example to set this tag. The structure picked here is the monolayer CrI$_3$. To achieve an AFM configuration, a square lattice with four Cr atoms is built as follows:

• Antiferromagnetic configuration setting: Cr1 ($\uparrow$) / Cr2 ($\downarrow$) / Cr3=Cr1 ($\uparrow$) / Cr4=Cr2 ($\downarrow$)

• All I atoms are non-magnetic.

• QE scf input card:

   &CONTROL
      calculation='scf'
      prefix='CrI3'
      outdir='./tmp/'
      pseudo_dir='./pseudo/'
      etot_conv_thr=1.0d-05
   /
   &SYSTEM
      ibrav=0
      nat=16
      ntyp=3
      ecutwfc=60
      ecutrho=720
      occupations='smearing'
      smearing='mp'
      degauss=0.02
      nspin=2
      starting_magnetization(1)= 3  !note that ntype=3
      starting_magnetization(2)=-3
      starting_magnetization(3)= 0
    /
    &ELECTRONS
      conv_thr=1.0d-8
      mixing_beta=0.7
      electron_maxstep=200
    /
    ATOMIC_SPECIES
      Cr1  51.996 cr_pbe_v1.5.uspp.F.UPF
      Cr2  51.996 cr_pbe_v1.5.uspp.F.UPF
      I    126.9045 I.pbe-n-kjpaw_psl.0.2.UPF
    ATOMIC_POSITIONS crystal
      Cr1  0.0000000000  0.0000000000   0.3304567040
      Cr2  0.0000000000  0.3333333430   0.3297766150
      Cr1  0.5000000000  0.5000000000   0.3304567040
      Cr2  0.5000000000  0.8333333730   0.3297766150
      I    0.1495049890  0.1672649980   0.4083212910
      I    0.6495050190  0.6672649980   0.4083212910
      I    0.1743501420  0.4911199810   0.4083212910
      I    0.6743501420  0.9911199810   0.4083212910
      I    0.6761449580  0.3416150210   0.4083212910
      I    0.1761449580  0.8416150210   0.4083212910
      I    0.8504950400  0.1660683450   0.2519120570
      I    0.3504950400  0.6660683160   0.2519120570
      I    0.3256500360  0.3422133330   0.2519120570
      I    0.8256500360  0.8422133330   0.2519120570
      I    0.8238549830  0.4917183820   0.2519120570
      I    0.3238549830  0.9917184110   0.2519120570
    CELL_PARAMETERS angstrom
      6.8670001030       0.0000000000       0.0000000000
      0.0000000000      11.8939924240       0.0000000000
      0.0000000000       0.0000000000      20.0000000000
    K_POINTS automatic
      4 2 2 0 0 0
  

• Total magnetization in each electronic step:

• Once you know how to do the self-consistent calculation, all left calculations are easily performed.