[Pw_forum] Linear response method for J

[Matteo Cococcioni]

Dear Pietro,

keep in mind that the calculation of J with linear response is quite
tricky. In fact, as we mention in the paper, it only work if you start from
a non magnetic ground state. with a magnetic ground state, instead, gives
quite suspicious results. the reason is, I think, that the energy is not
variational with respect to the magnetization m.
For CuO we only measured J from GGA as the GGA ground state is non
magnetic.

hope this helps.

best,

Matteo


On Mon, Jun 30, 2014 at 4:51 PM, Pietro Bonfa' <pietro.bonfa at fis.unipr.it>
wrote:

> Dear PWscf users,
>
> I'm trying to estimate J with the linear response approach discussed in
> the article by Himmetoglu and colleagues (PRB 84, 115108 (2011) ) for a
> T' La2CuO4 compound.
> I already obtained a reasonable value for U and now, staring from the
> GGA ground state, I'm perturbing onsite magnetizations.
>
> I get rather strange trends that you can find here (links to images at
> the bottom of the page):
>
> http://pad.hdc.pw/p/EPtfu67vWX
>
> An example is also in attachment (I preferred not to add too many/heavy
> attachments to the email. The above link should survive long enough and
> contains the input and output files and other useful informations).
>
> Can someone give me a hint on the (in my opinion) odd results obtained
> for atoms 10, 38, 66 and 94 (they are the atoms of the other, i.e. not
> perturbed, antiferromagnetic sublattice in the same CuO plane).
>
> Should I trust the results obtained starting from those derivatives?
>
> Thanks in advances for your time,
> kind regards,
> Pietro Bonfa'
>
> --
> Pietro Bonfa' - PhD student
> Dipartimento di Fisica e Scienze della Terra "Macedonio Melloni"
> Viale delle Scienze 7A
> 43124 Parma - Italy
>
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