[Wien] about calculating the magnetic moment

[Stefaan Cottenier]

> I have no experience using WIEN2k. I wonder how the magnetic moment of an
atom is
> calculated in WIEN2k. Is it just the difference between the spinup and
spindown densities
> within the MT sphere?

Yes (for the spin moment, WIEN2k can calculate the orbital moment as well).
Apart from these magnetic moments for one atom, you can also find the (spin)
magnetic moment for the entire unit cell: here not only the difference
inside all spheres is taken into account, but also the contribution from the
region in between the spheres.

> If so, how to handle the MT radius? As I know, the MT radii in LAPW
calculations are
> usually adjustable in order to achieve a compromise between the accuracy
and the efficiency.

It is true that these spin moments depend a little bit on the sphere size.
But usually the variations are of the order of 5% or less if the MT radii
are varied within a window of reasonable values. For most purposes, this is
enough (in experiment you have the same problem, after all: to which atom do
you assign a spin moment contribution from a point that is between two
atoms?). Only in rare cases where you have a considerable moment in the
interstitial region, the sphere size dependence can be larger. The spin
moment of the entire unit cell should not depend on the sphere sizes at all.

Stefaan