[Wien] exchange coupling constants calculations

[Rocquefelte]

Dear Vincent,

The rule is quite simple. Let's take the example of a monoatomic linear 
chain.
To obtain the J parameter coupling two adjacent magnetic centers, you 
simply have to do 2 calculations:

- one with the ferromagnetic order: FM
- one with the antiferromagnetic order: AFM

You will then obtain two total energies, i.e. E(FM) and E(AFM).

Considering an Heisenberg Hamiltonian, you have:

E(FM) = N²/4 * (-J)

and

E(AFM) = N²/4 * (+J)

Then E(AFM) - E(FM) = N²/4 * (2*J) = N²/2 * J

where N is the number of unpaired electrons on the magnetic center.

For example, for N = 1:

J = 2 * (E(AFM) - E(FM))

The present example is very simple and you could imagine that for more 
complex structures it will be more difficult to realize a mapping 
analysis. Then the idea is:
- to use more magnetic orders than unknown J parameters
- to do a least-square procedure to find the J values ...

Here is and example of calculations I did with Peter and Karlheinz on CuO:

http://iopscience.iop.org/0953-8984/22/4/045502

If you do not have access to the paper, I could send it to you.

Regards

Xavier





Le 18/05/2011 12:31, Linux PC a écrit :
> Dear Xavier,
>
> Thank you very much for the answer! I actually was looking through the 
> manual before, unfortunately, did not succeed in finding any 
> information on exchange interactions. Would you know, or may be other 
> users, if any practical manual exists for calculating of J.
>
> Thank you!
> Vincent
>
> > Date: Wed, 18 May 2011 07:24:52 +0200
> > From: Xavier.Rocquefelte at cnrs-imn.fr
> > To: wien at zeus.theochem.tuwien.ac.at
> > Subject: Re: [Wien] exchange coupling constants calculations
> >
> > Dear Vincent,
> >
> > Yes for sure. To estimate magnetic exchange coupling parameters you
> > need to do a mapping based on total energies of different magnetic
> > orders. WIEN2k allows to have total energies with high accuracy and
> > using different functionals (depending of the system you are
> > considering). So yes, using WIEN2k to estimate J values is an
> > excellent choice.
> >
> > Regards
> >
> > Xavier
> >
> >
> >
> > "Linux PC" <linuxfarm3m at hotmail.fr> a écrit :
> >
> > >
> > >
> > > Dear Dr. Blaha and Wien2k users,
> > >
> > > Is it possible to use the Wien2k to calculate j magnetic exchange
> > > coupling constants?
> > >
> > > Thank you very much,
> > > Vincent
> > >
> >
> >
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> > Wien at zeus.theochem.tuwien.ac.at
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>
>
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