how can we set the value of " initial_scaled_spin"

[alan]

hi everyone,
    i mean if we want to calculate the spin depended properties.so we should give an initial spin to the structure.i am confused with the  value of " initial_scaled_spin" .just like the tutorial show the graphene ribbon initial_scaled_spin = [ 1., 1., 0., 0., 0., 0., -1., -1., 0., 0. ].i do not know why he setlike this.and if i set the value as initial_scaled_spin = [ 1., 0., 0., 0., 0., 0., 0., -1., 0., 0. ]orinitial_scaled_spin = [ 1., -1., 0., 0., 0., 0., 1., -1., 0., 0. ].is that ok? i want to know what does the initial_scaled_spin mean.
thank for your help.

[zh]

The setup for the initial spin values of graphene ribbon may be demonstrated for a configuration that only the carbon atoms at the edges of ribbon are specified by the non-zero spin values. This is reasonable because there are dangling bonds at these edged carbon atoms. Now many theoretical studies have shown the edges of graphene ribbon mainly contribute to its magnetism properties.

and if i set the value as initial_scaled_spin = [ 1., 0., 0., 0., 0., 0., 0., -1., 0., 0. ]orinitial_scaled_spin = [ 1., -1., 0., 0., 0., 0., 1., -1., 0., 0. ].is that ok? i want to know what does the initial_scaled_spin mean.

Do you know what are the ferromagnetic, anti-ferromagnetic, or ferrimagnetic states (or configurations) for a magnetic system or compound? If yes, your questions may be answered by yourself. If no, please pick up a solid state physics book or visit here to learn what are the types of magnetism:
http://www.msm.cam.ac.uk/doitpoms/tlplib/ferromagnetic/printall.php

The value of "initial_scaled_spin" defines the initial magnetic moment of atom.  Different setup for the "initial_scaled_spin"s of atoms in system under study would initialize the type of magnetism of your system.

[alan]

actually， i know a little about  ferromagnetic, anti-ferromagnetic, or ferrimagnetic states ,but i am not sure about the  magnetism properties of graphene ribbon. i want to know if i want to get an  ferromagnetic system.the initial_scaled_spin = [ 1., 1., 0., 0., 0., 0., -1., -1., 0., 0. ] the orinitial_scaled_spin = [ 1., -1., 0., 0., 0., 0., 1., -1., 0., 0. ].and initial_scaled_spin = [ 1., 0., 0., 0., 0., 0., 0., -1., 0., 0. ]which one is ture?or both ok ? i read some correlative papers,but i can get the conclusion for the settings in atk calculation.

[zh]

If it is  a bulk or molecule system, from its total energies for different magnetic states one may find which magnetic state is more energetically stable. It is hard to answer which one is more preferable before performing the total energy calculations.

If you just want to study the ferromagnetic state of graphene ribbon, you had better specify the same non-zeros value to the initial spins of all edged carbon atoms, i.e,
[1, 1, 0, 0, .....,  1, 1, 0,0] where the atoms with non-zero spin values are at the edges of graphene ribbon.

[Tom]

 hello
 When I calculate the two probe system with initial_scaled_spin,I have the same trouble .I want to calculate the ferromagnetism about the graphene nanoribbon,but I didn't know how add the spin to the two probe and scaled area.Do I need add the spin to the edge of the ribbon only? No spin in the center of the ribbon?Need I calculate total energy of many situations to centain the most steady states?
And I want to know whether it change the spin on every atoms when we have a self-consistent calculation.
 Thanks a lot.

[zh]

For a homogeneous system (i.e., consisting of same element) with ferromagnetic state, it means that the spin moment for each atom is same. In this situation, the initial spin of each atom had better be assigned with a same value.

For graphene nanoribbon, several theoretical studies have demonstrated that the spin moments of this system mainly comes from the spin-polarization of edge states. This means that it is reasonable to initialize the spin moment of only the edge carbon. At least, you should consider two cases: i) the parallel spin configuration (i.e., ferromagnetic state) for the two edges of a graphene nanoribbon; ii) the anti-parallel spin configuration (anti-ferromagnetic state) the two edges of a graphene nanoribbon.