### Non-collinear magnetism setup

To configure a Fleur calculation incorporating non-collinear magnetism, some parameters have to be set in the calculationSetup section and further parameters have to be set for each atomGroup in the atomGroups section. In each of these sections nocoParams elements have to be added. Templates with default parameters are generated by using the input generator with the -explicit or -noco command line options.

An example for the nocoParams element in the calculation setup section is:

<nocoParams l_ss="F" l_mperp="T" l_constr="F" mix_b=".00000000">
<qss>.0000000000 .0000000000 .0000000000</qss>
</nocoParams>

The following attributes have to be set here:

Attribute Description
l_ss This boolean switch is used to activate spin-spiral calculations.
l_mperp Here the output of the magnetization perpendicular to the chosen axis can be activated.
l_constr Switch this on to constrain the magnetic moments.
mix_b This is a mixing factor. If l_constr is set to true then the constraint field is mixed. In this case mix_b="0.5" should work fine. In the case of an atom with l_relax being set to true the input/output-directions of the moments are mixed. Here you can choose mix_b > 1 (e.g. 4).

The enclosed XML element <qss> is used to define the spin spiral vector in reciprocal lattice vectors.

An example for the nocoParams element in each atomGroup is:

<nocoParams l_relax="F" alpha="Pi/4.0" beta="Pi/2.0"
b_cons_x=".00000000" b_cons_y=".00000000"/>

The following attributes have to be set here:

Attribute Description
l_relax This has to be set to true to relax the directions of the magnetic moments at the associated atoms.
alpha The 1st angle that determines the magnetic structure. It is equal to $\varphi$ in spherical coordinates.
beta The 2nd angle that determines the magnetic structure. It is equal to $\vartheta$ (measured from the z axis) in spherical coordinates.
b_cons_x, b_cons_y These are the constraint fields in x and y direction. They are determined self-consistently if l_constr is set to true.