[Wien] Orientation of Atomic Spin Moments

[Robert Laskowski]

> Thanks for the comments. Let me back up a little bit from the
> ambitious orientation thing. In stead, I would like to study the two
> magnetic atoms (the unit cell contains
> many other non-magnetic atoms; these 2 magnetic atoms are close to
> each other and well separated from the magnetic ones in the next unit
> cell) using the Heisenberg-like model: H= J  S1 . S2  ------ So my 2
> important questions will be:  1) How do I figure out the atomic spin
> Sa? I have guessed of using n(up) - n(dn)
> as S but I don't understand why it works this way. Sa*(Sa+1) is the
> eigenvalue of the atomic spin operator S^2, where S is the sum of
> electron spin (vector) operators.
> 2) Is there a way to calculate J without going to noncolinear?
>

1) you calculate only S_z.
2) run ferromagnetic and antiferromagnetic calculations, and get J from 
    difference of total energies.






-- 
Dr Robert Laskowski

Vienna University of Technology, 
Institute of Materials Chemistry, 
Getreidemarkt 9/165-TC, A-1060 Vienna

tel. +43 1 58801 15678
Fax  +43 1 58801 15698