Spin dependent calculations were performed for Fe and FeO which are
ferromagnetic and antiferromagnetic respectively. The calculations
were performed using a spin dependent GGA and non-linear core
corrections for the iron pseudopotential. The results of these
calculations and the spin population analysis may be seen in Table
.
| Material | Total | Integrated |  | Fe | O | |
Spin (  ) | |Spin| ( ) |  |  |
Spin ( ) | Spin ( ) | |
| Fe | 2.43 | 2.56 |  |  | 1.22 | - |
| FeO | 0.00 | 7.66 |  | | 3.71,-3.71 | 0.23,-0.23 |
From the data for Fe, we can see that the calculations correctly
predict the ferromagnetic behaviour, with the spin and spin modulus
having similar values. The spin of 1.22 per atom gives a
predicted value for the magnetisation at T=0K of 1921 Gauss which
compares favourably with the experimental value of 1752 Gauss. The
antiferromagnetic behaviour of FeO is also correctly predicted. Two
values are found for the spin on the iron atoms and oxygen atoms which
are equal in magnitude but opposite in direction. The sign of the spin
alternates between planes along the direction in which the spin is
resolved. In addition, the magnitude of the spin on the iron atoms is
found to be much higher than that on the oxygens. This picture,
obtained from the Mulliken spin populations, is confirmed if we examine
the spin density as shown in Figure .
Figure: Spin density isosurface plot for a unit cell of
FeO. The yellow and red isosurfaces represent spin up values in order
of increasing magnitude, the cyan and blue isosurfaces represent spin
down values in order of increasing magnitude. Iron and oxygen atoms
are blue and red respectively.