Spin with Abinit

An example of visualising antiferromagnetic spin in FeO with Abinit.

The input files used for abinit were:

FeO.in

acell 16.372587151 8.18629357548 8.18629357548
rprim
      0.00000000000  0.50000000000  0.50000000000
      0.50000000000  0.00000000000  0.50000000000
      0.50000000000  0.50000000000  0.00000000000

ntypat 2
znucl  8 26
natom 4
typat  1  1  2  2
xred
  0.25  0.5  0.5
  0.75  0.5  0.5
  0  0  0
  0.5  0  0

nsppol 1
nspden 2
spinat  0 0 0.000000  0 0 0.000000  0 0 2.000000  0 0 -2.000000
      
kptopt 1
ngkpt 1 3 3
nshiftk 1
shiftk 0.25 0 0

ecut 520 eV
toldfe 4e-05 eV

chksymbreak 0
chkprim 0

FeO.files

FeO.in
FeO.out
none
FeO
tmp
O.psp8
Fe.psp8

Pseudopotentials

$ curl -O http://www.pseudo-dojo.org/pseudos/nc-sr-04_pbe_standard/O.psp8.gz
$ gunzip O.psp8.gz
$ curl -O http://www.pseudo-dojo.org/pseudos/nc-sr-04_pbe_standard/Fe.psp8.gz
$ gunzip Fe.psp8.gz

Running Abinit

$ abinit < FeO.files > FeO.log

Visualising the result

One can quickly check that an antiferromagnetic spin state has been produced.

$ c2x -vs --null FeO_DEN
Rescaling spin from Bohr^-3 to A^-3 and calculating net spin
Found 3D data for Spin
  min=-3.27618 max=3.27618 sum=-7.30971e-13 int=-1.07466e-15 int|s|=7.07998
  (integral is e per cell for charge and spin densities)

The data contains signficant positive and negative values, and appears to have almost perfect inversion symmetry, in that (approximately) min=-max and sum=0. That the integral of the modulus of the spin is given as 7.08 implies a magnetic moment per Fe atom of 3.54μ_B, which is within the range of published values - a 2016 JCTC paper quotes an experimental range of 3.3 to 4.2μ_B, and a calculated range of 3.4 to 4.3μ_B.

To visualise:

$ c2x -vs -X='(8.664,0,0)(0,8.664,0)(0,0,8.664)' --xsf FeO_DEN FeO_spin.xsf

Here we have chosen to expand from the original four-atom cell to a unit cell which is itself cubic, in order to make the visualisation clearer. And whereas most of the images on this site are from XCrysDen, this time VESTA has been used.

FeO and spin density

The Fe atoms are gold, the O atoms small and red, and the isosurfaces of the spin density can be seen to be enclosing the Fe atoms, and that the Fe atoms are in layers of alternating sign of spin density, shown by the yellow and cyan colouring of the isosurfacs.