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 .
|Spin ( )|||Spin| ( )||Spin ( )||Spin ( )|
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.