Equally probable FM and AFM states

[jai]

Dear all,

I am doing selective functionalization of silicene nanoribbons via non metallic elements (O, P etc.).
Some of the results are showing that ferromagnetic (FM) and anti-ferromagnetic (AFM) states have exactly equal total energy which is however more negative than that of its non-magnetic phase.
Does it indicates for a paramagnetic ground state or should I explore with other functionals?
Currently I am using GGA.

[zh]

Have you checked the spin density distributions in your so-called "FM" and "AFM" states?  If the energies of these two states are identical, you may need to check their electronic structures.   

If the ribbons are wide enough, the interaction between two edge spins could be neglected. In that case,  what you treat is the spin along one edge. 

This is also applicable to the spin induced by two isolated impurities.

[jai]

Hi,
Thanks for the valuable suggestions.
I checked for the electronic structures and found that both of these are also identical to each other.

The considered zigzag ribbons are having width Nz = 8 to 16.  What is the significance of considering spin along one edge?
Does it mean that there may be no magnetic coupling between edges?
Is there any possibility of paramagnetism?

[zh]

Probably there are no spin coupling between two edges because edge spin rapidly fade toward the ribbon center region. The spin coupling may exist when the ribbon width is very narrow.

"What is the significance of considering spin along one edge?"
This may be what you need to think deeply about such problem for the research purpose.
Since the spin-polarization is induced by the "doping"of non-metallic elements (P and O, etc) along the edge, it may be more important to think about the interaction of such spin induced by these impurities along one edge.

"Is there any possibility of paramagnetism?"
It may be hard to say the existence of paramagnetism in your case because each edge is strongly spin-polarized.

[berlin]

errors of total energy calculation, which are intorduced from LCAO basis, may be several hundred meV. You'd better use vasp or other code based  on plane wave basis to calculate total energy!