[Wien] magnetic susceptibility for a ferromagnetic metal or for a ferromagnetic semiconductor

Thu Jul 20 18:12:29 CEST 2017

Thank you very much for your detailed answer

What I understood from what you wrote is that the DFT does not accurately
estimate the magnetic susceptibility. honestly what is encouraged me to
take an interest in this property is the paper of Prof. Robert Laskowski
and Prof Peter Blaha  (doi:  10.1021/acs.jpcc.5b05947
<https://dx.doi.org/10.1021%2Facs.jpcc.5b05947>) where they compared their
results for many metals and found values very similar to the experimental
ones.

Now I do not know is what the estimate of molar magnetic susceptibility is
possible with wien2k or its estimate is not always accurate.

2017-07-20 16:54 GMT+02:00 pieper <pieper at ifp.tuwien.ac.at>:

>
>
> From what I have understood from userguide and Prof P Blaha's replies;
>>>> For semiconductor and insulator; there is the orbital part of the
>>>> magnetic susceptibility only
>>>> but for the metals there is also the spin part
>>>>
>>>
> No! This is not correct. Let me expand a little on my view of this topic
> in the hope to clarify the problem at least somewhat:
>
> In a nutshell, you want Wien2k to find the state minimizing the total
> energy of some solid because you suspect that this is the state whose
> properties you observe in some experiment, and someone told you that DFT is
> the method of choice to do the search.
>
> Magnetic moments contribute M*B to that energy with M and B being vectors
> in a scalar product. In a first approximation two contributions from
> electrons to M can be considered separately, namely the spin moment, and
> the moment from an orbital momentum (or the current associated with a
> non-zero orbital momentum). Both parts contribute to the energy in the
> field. That is why Peter Blahas very first statement was:
>
> A magnetic field influences the spin and orbital degrees of freedom.
>
> It always does. Both contributions to M. No matter wether you have an
> insulator or a metal. The influence on specific properties you are
> interested in may be too small to bother, but somewhere else it will show
> up.
>
> There are different ways to tell Wien2k where to look for the state with
> minimum energy in an applied magnetic field (or electric field). This is
> where symmetry enters stage: Wien2k searches the state with lowest energy
> in the subspace compatible with the symmetries specified by the input
> files. The symmetry of the crystal structure is in the struct file.
> Concerning magnetic moments you can tell Wien2k to
>
> - consider only states that are symmetric with respect to spin, i.e. do a
> non-spin-polarized calculation. Doesn't make sense if you are interested in
> the effect of a magnetic field or want to model ferromagnets, but for the
> majority of materials and properties it's perfect to save time and
> calculate just spin +1/2, then carry the result over to spin -1/2.
>
> - take into account the two spin channels separately, i.e. do a
> spin-polarized calculation, and introduce B as 'orbital potential' in the
> program orb. Note that a field you put into .inorb acts on the electrons in
> the single atomic shell you specify, and only for the part within the
> muffin-tin radius. Everything else is indirectly adjusted according to
> interactions. I am (of course) with Peter Blaha: One can expect very
> reasonable estimates for field induced moments at the given shell, at least
> if the field induced polarization of electrons not affected by .inorb is
> small. The option also shows a Zeeman splitting of spin-up and -down bands
> due to the interactions, but I expect that depending on the case this can
> rapidly turn into a paedagogical example rather than an estimate of the
> spin susceptibility.
>
> - take into account the fact that the energy contribution M*B quite
> possibly reduced symmetry. M as well as B are vectors, after all, and
> transform as such under symmetry operations. You can switch on spin-orbit
> interaction to tell Wien2k about this. (Be aware that Wien2k always assumes
> that M and B are colinear). As Gerhard Fecher pointed out, a reduced
> symmetry in a magnetic field is NOT taken into account in the orb program.
> With only the orb option active Wien2k may search the needle (the energy
> minimum) in a completely wrong haystack (subspace).
>
> - do a calculation of the linear response of the all-electron wave
> function (representing spins AND orbital moments) to an applied field. As I
> understand it this is what the NMR module does. However, it calculates only
> the local response at the nuclei, not the integrated macroscopic
> susceptibility.
>
> Note that all this does not represent anything like the macroscopic
> susceptibility you will detect with a ferromagnetic (or any other
> magnetically ordered) material in your magnetometer. The susceptibility in
> these cases even at zero Kelvin (where DFT arguably applies) is dominated
> by things the spins can and will do, but Wien2k is completely unaware of
> (magnons, domain walls ...).
>
> Finally, don't take the UG or this mailing list as a substitute for a
> textbook. That is not their intention. Follow the advice of Prof. Fecher
> and read up on the subject of magnetism in solids. Perhaps start with
> something on solid state physics in general, not a specialized treatment of
> magnetism. Personally I like the introduction to Solid State Physics by
> Ashcroft and Mermin.
>
> Good luck
>
> ---
> Dr. Martin Pieper
> Karl-Franzens University
> Institute of Physics
> Universitätsplatz 5
> A-8010 Graz
> Austria
> Tel.: +43-(0)316-380-8564
>
>
> Am 19.07.2017 16:02, schrieb karima Physique:
>
>> From what I have understood from userguide and Prof P Blaha's replies;
>> For semiconductor and insulator; there is the orbital part of the
>> magnetic susceptibility only but for the metals there is also the spin
>> part and I ask Prof. P Blaha and Prof Gerhard Fecher  to confirm this
>> answer or to correct it.
>>
>> 2017-07-19 13:34 GMT+02:00 Wien2k User <wien2k.user at gmail.com>:
>>
>> I did not underestimate his answer and the proof I thanked him and I
>>> apologize if I did not convey my message well
>>>
>>> 2017-07-19 12:48 GMT+02:00 Wien2k User <wien2k.user at gmail.com>:
>>>
>>> Dear Fecher, Gerhard
>>>
>>> You can answer me directly instead of asking me all these questions
>>> otherwise I thank you for your answer and I will look for this book
>>> to read it and in the meantime I will wait for the answers of the
>>> users and prof P. Blaha that I much prefer.
>>>
>>> 2017-07-19 3:47 GMT+02:00 Wien2k User <wien2k.user at gmail.com>:
>>>
>>> dear wien2k user
>>>
>>> From the userguide we find how to calculate the magnetic
>>> susceptibility for an insulator or a paramagnetic metal but how to
>>> calculate the magnetic susceptibility for a ferromagnetic metal or
>>> for a ferromagnetic semiconductor?
>>>
>>
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