[QE-users] constrained magnetization with non-colin and spin-orbit

Mon Jan 18 11:57:27 CET 2021

Dear Cyrille,

Il giorno lun 18 gen 2021 alle ore 11:42 BARRETEAU Cyrille <
cyrille.barreteau at cea.fr> ha scritto:

> Dear Matteo,
> Non collinear calculations are usually very difficult to converge with QE
> (usually codes based on localized basis set are easier to converge since I
> guess there are less degrees of freedom..).
> This is even more difficult in finite systems such as clusters or
> molecules where you can often have multiple magnetic states.
>

Yes, in fact this is also my case: many magnetic states.

> Did you try to perform non-collinear calculations without SOC? Just to
> check that collinear configurations converge and are independent of the
> magnetization angle?
>

I only got convergence with SOC. without SOC I haven't tried yet but I
will. I have to go back to the scalar-relativistic PP for that, right?

Thanks,

Matteo

> Cyrille
>
> ========================
> *Cyrille Barreteau*
> CEA Saclay, IRAMIS, SPEC Bat. 771
> 91191 Gif sur Yvette Cedex, FRANCE
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +33 1 69 08 38 56 /+33  6 47 53 66 52  (mobile)
> email:     cyrille.barreteau at cea.fr
> Web:     http://iramis.cea.fr/Pisp/cyrille.barreteau/
> ========================
> ------------------------------
> *De :* users [users-bounces at lists.quantum-espresso.org] de la part de
> Matteo Cococcioni [matteo.cococcioni at unipv.it]
> *Envoyé :* lundi 18 janvier 2021 11:05
> *À :* Quantum ESPRESSO users Forum
> *Objet :* Re: [QE-users] constrained magnetization with non-colin and
> spin-orbit
>
> Dear Cyrille,
>
> thanks for your reply and advice.
>
> Il giorno lun 18 gen 2021 alle ore 10:25 BARRETEAU Cyrille <
> cyrille.barreteau at cea.fr> ha scritto:
>
>> Dear Matteo
>>
>> If I understand well you want to calculate the magnetic anisotropy of a
>> magnetic molecule.
>>
>
> Yes, that's correct
>
>
>> I am not sure I have understood well the way you proceed when you say
>> that you "start" from a collinear lsda.
>>
>>
> Well, I tried to start a non collinear calculation of this system from
> scratch, but I could never achieve convergence. The convergence with lsda
> is much more robust and using tot_magnetization I could achieve both a
> ferromagnetic and an antiferromagnetic ground state. Then I tried to use
> the charge-density of these ground states to initialize the non-collinear
> calculation (of course after updating the Mo PP to its fully relativistic
> version) with spin-orbit. This way I manage to converge to the same AFM and
> FM ground state with the non-collinear calculation. Now I want to use these
> calculations as starting points to take the magnetic moments away from the
> z direction to which they are (anti)aligned.
>
>
>> I would say that you can try two strategies:
>>
>> i) using the force theorem as implemented in QE (one scf lsda calculation
>> and then nscf with SOC starting from different theta angles..)
>>
>
> ok, I hadn't thought of this. Maybe it's sufficient to estimate the MAE.
> If you initialize just the theta angle (angle1) will the modulus of the
> magnetic moment be preserved with respect to the lsda or collinear ground
> state it starts from? How does the code choose the angle phi (angle2) in
> this case? In presence of SOC this also might make a difference and
> contribute to the MAE (unless the system has a cylindrical symmetry around
> the easy axis, which is not my case).
>
>
>> ii) use the magnetic constraint with penalization parameter lambda and
>> perform a scf calculation. It will be more delicate but maybe more precise
>> (not sure since you might face convergence problems)
>>
>>
> This is what I was trying to do (see above, also): I am trying to change
> angle1 with lambda. I wanted to do a scf calculation to leave the system
> free to chose angle2. But the convergence is very delicate. Actually there
> seems to be no finite contribution to the potential from the constraint, so
> the calculation goes on for a while without changing the angles from their
> starting value and then suddenly crashes (not sure why). It seems that the
> variable pointlist is never different from 0 in my case which causes the
> potential to be insensitive to lambda. But I haven't yet understood why.
>
> thanks again.
>
> Best regards,
>
> Matteo
>
>
>
>> best
>> Cyrille
>>
>>
>>
>> ========================
>> *Cyrille Barreteau*
>> CEA Saclay, IRAMIS, SPEC Bat. 771
>> 91191 Gif sur Yvette Cedex, FRANCE
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> +33 1 69 08 38 56 /+33  6 47 53 66 52  (mobile)
>> email:     cyrille.barreteau at cea.fr
>> Web:     http://iramis.cea.fr/Pisp/cyrille.barreteau/
>> ========================
>> ------------------------------
>> *De :* users [users-bounces at lists.quantum-espresso.org] de la part de
>> Matteo Cococcioni [matteo.cococcioni at unipv.it]
>> *Envoyé :* dimanche 17 janvier 2021 11:09
>> *À :* Quantum ESPRESSO users Forum
>> *Objet :* [QE-users] constrained magnetization with non-colin and
>> spin-orbit
>>
>>
>> Dear all,
>>
>> I am trying to run some calculations on a molecule with two magnetic ions
>> (Mo) and I want to use the non collinear spin with spin-orbit to calculate
>> the energy needed to change their direction. Starting from a collinear
>> (lsda) calculation I managed to converge the non-collinear one in a
>> ferromagnetic configuration, with magnetic moments aligned along z. Now I
>> am using this ground state as starting point for a calculation where one or
>> both spins are somehow deviated from the z direction. Following the
>> instructions in INPUT_PW I am using the following settings (in &system):
>>
>>     noncolin = .true.
>>     lspinorb=.true.
>>     angle1(1) = 30.0
>>     angle1(2) = 30.0
>>     constrained_magnetization = 'atomic direction'
>>     lambda = 1.0
>>
>> where species 1 and 2 correspond to the two Mo, angle1 is the angle I
>> want to have between z and the final magnetization, lambda is the strength
>> of the quadratic constraint.
>>
>> If I start from the potential of the ground state with the magnetization
>> along z, the code starts with no problem and even pretends to converge for
>> a number of iterations. Then suddenly the energy explodes and the code
>> crashes saying that there are too many not converged eigenvalues.
>> While it seems converging nothing relevant seems to happen to angles: the
>> constraint energy remains almost the same and the magnetization of both
>> atoms maintains its original direction (aside small fluctuations). The same
>> behavior is observed independently from the value of lambda (which is very
>> strange) and beta (the mixing parameter).
>>
>> looking into the code (add_bfield.f90) the implementation of the
>> constraint seems fine, as far as I can tell (except that the code tries to
>> constraint all magnetic moments once a lambda is present, which I fixed),
>> and the potential seems to get a term from the constraint on magnetization.
>> So I would expect it to do something.
>>
>> Does anyone have any experience with this type of calculations? What am I
>> missing or not doing right? Thanks in advance for any help/advice.
>>
>> Best regards,
>>
>> Matteo
>>
>> --
>> Matteo Cococcioni
>> Department of Physics
>> University of Pavia
>> Via Bassi 6, I-27100 Pavia, Italy
>> tel +39-0382-987485
>> e-mail matteo.cococcioni at unipv.it <lucio.andreani at unipv.it>
>> _______________________________________________
>> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
>> users mailing list users at lists.quantum-espresso.org
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>
>
>
> --
> Matteo Cococcioni
> Department of Physics
> University of Pavia
> Via Bassi 6, I-27100 Pavia, Italy
> tel +39-0382-987485
> e-mail matteo.cococcioni at unipv.it <lucio.andreani at unipv.it>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users

-- 
Matteo Cococcioni
Department of Physics
University of Pavia
Via Bassi 6, I-27100 Pavia, Italy
tel +39-0382-987485
e-mail matteo.cococcioni at unipv.it <lucio.andreani at unipv.it>
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