[Pw_forum] Constrained magnetic calculation
Varadharajan Srinivasan
varadharajan.srinivasan at gmail.com
Mon Mar 10 18:59:04 CET 2014
Dear Cyrille,
I just made an alteration to add_bfield.f90 only including constraint
energy contributions from the magnetic ions. This I expect is an indirect
way of setting the lambdas for other atoms to zero albeit not very general.
It's a Fe3+ system which in the high-spin state should have 5 unpaired
electrons. While I don't expect to achieve that ideal value (actually I
don't when doing a regular unconstrained calculation biased towards the
high-spin state) I am only testing the constraint optimisation.
Thanks,
Vardha.
On Sun, Mar 9, 2014 at 2:24 AM, BARRETEAU Cyrille
<cyrille.barreteau at cea.fr>wrote:
> Dear Vardha
>
> For the moment in the actual version of pw there is only one lambda which
> applies to all types of atoms.
> I have no idea of the type of systems you are looking at but a target
> moment of 5 for Fe is just "crazy".
> So this is not surprising that you need such large values of lambda to
> converge towards this solution.
> I am even surprised that you managed to get a solution!
>
>
> Cyrille
>
>
> -----------------------------------------------------------------------------------------------------------
> *Cyrille Barreteau*
> CEA Saclay, IRAMIS, SPCSI, Bat. 462
> 91191 Gif sur Yvette Cedex, FRANCE
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> phone: +33 (0)1 69 08 29 51 / +33 (0)6 47 53 66 52
> fax : +33 (0)1 69 08 84 46
> email: cyrille.barreteau at cea.fr
> Web: http://iramis.cea.fr/Pisp/cyrille.barreteau/
>
> -----------------------------------------------------------------------------------------------------------
> ------------------------------
> *De :* pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] de la part
> de Varadharajan Srinivasan [varadharajan.srinivasan at gmail.com]
> *Envoyé :* samedi 8 mars 2014 20:02
>
> *À :* PWSCF Forum
> *Objet :* Re: [Pw_forum] Constrained magnetic calculation
>
> Dear Cyrille,
>
> This is what we ended up doing setting all lambdas except the two
> magnetic ions to zero. However, the constrained moments still seem to
> converge rather slowly with lambda. I attach the plot below. We are also
> testing this on a Fe-Cr system. We set the target moments to 5 for Fe and
> -3 for Cr (antiferromagnetic arrangement). Is there any physical reason why
> this would happen?
>
> Best,
> Vardha
>
>
> On Thu, Mar 6, 2014 at 3:31 PM, BARRETEAU Cyrille <
> cyrille.barreteau at cea.fr> wrote:
>
>> In fact it can be very useful to constrain just some atoms and not all
>> of them. We used that option a few years ago when studying the magnetic
>> properties of Cr atoms in a Fe matrix. At that time we did it by hacking
>> ad_bfield.f90. An alternative solution would be to define a different
>> lambda(i) for each type of atom and set lambda(i)=0 for the atom which do
>> not need to be constrained.
>>
>> regards
>> Cyrille
>>
>>
>> -----------------------------------------------------------------------------------------------------------
>> *Cyrille Barreteau*
>> CEA Saclay, IRAMIS, SPCSI, Bat. 462
>> 91191 Gif sur Yvette Cedex, FRANCE
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> phone: +33 (0)1 69 08 29 51 / +33 (0)6 47 53 66 52
>> fax : +33 (0)1 69 08 84 46
>> email: cyrille.barreteau at cea.fr
>> Web: http://iramis.cea.fr/Pisp/cyrille.barreteau/
>>
>> -----------------------------------------------------------------------------------------------------------
>> ------------------------------
>> *De :* pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] de la
>> part de Gabriele Sclauzero [gabriele.sclauzero at mat.ethz.ch]
>> *Envoyé :* mercredi 5 mars 2014 10:38
>> *À :* PWSCF Forum
>> *Objet :* Re: [Pw_forum] Constrained magnetic calculation
>>
>> Dear Varadharajan,
>>
>> I do not know if it make sense or not in general, anyway this
>> possibility is not available at the moment. All atoms of atomic type i will
>> be constrained to have local magnetization equal to
>> starting_magnetization(i). However, you can try to edit the magnetic
>> constraint subroutine in PW/src/add_bfield.f90 to suit your needs.
>>
>> Regards
>>
>>
>> GS
>> Materials Theory, ETH Zurich
>>
>>
>> On 03/05/2014 05:25 AM, Varadharajan Srinivasan wrote:
>>
>> Dear Gabriele,
>>
>> To add to Paresh's question is it possible (and does it make sense) to
>> constrain the magnetisation of only a few atoms and not the others? While
>> the target here seems to be atoms 3 and 4 the other atoms are being made to
>> pay the price so to speak.
>>
>> One option, in the present framework, is to constrain the values of
>> magnetisation of all other atoms to their respective lambda=0 values. Could
>> this speed up the convergence with lambda?
>>
>> Thanks,
>> Vardha.
>>
>>
>> On Tue, Mar 4, 2014 at 7:18 PM, Gabriele Sclauzero <
>> gabriele.sclauzero at mat.ethz.ch> wrote:
>>
>>>
>>> What about the evolution of the constrained magnetization?
>>> (Please also make sure that the values specified in
>>> starting_magnetization make sense, as suggested by L. Paulatto Sir).
>>>
>>> My suggestion was to vary lambda in small steps (say 0.5). I'm surprised
>>> that you managed to converge the calculation with such high lambda values.
>>>
>>> Anyway, the constrain energy looks way too large, your system is
>>> probably still far from the target.
>>>
>>>
>>> GS
>>>
>>>
>>> On 03/04/2014 01:57 PM, paresh rout wrote:
>>>
>>> Respected Sclauzero sir,
>>> Thanks for your reply. According to your suggestion, I varied my
>>> Lambda value from 0,5,.......150 ry. Although calculated constrained
>>> energy are decreasing but upto 150 ry the constrained energy and the
>>> estimated scf accuracy are not the same order. Here I am providing my
>>> constrained energy with various lambda value.
>>>
>>> Lambda Constraint_Energy
>>> 0 0.00000000
>>> 5 36.93411685
>>> 10 69.54815816
>>> 15 6.65653915 estimated scf accuracy < 7.6E-13 Ry
>>> 20 7.88546052
>>> 25 8.88385707
>>> 30 9.71513061
>>> 35 10.42697250
>>> 40 11.05006563
>>> 45 11.60072229
>>> 50 12.08887057
>>> 70 13.54966033
>>> 80 14.05546257
>>> 90 14.45159513
>>> 100 14.75974550
>>> 110 14.99680383
>>> 120 15.17624003
>>> 130 15.30876396
>>> 140 15.40310437 estimated scf accuracy <
>>> 9.9E-13 Ry
>>> 150 15.46632278 estimated scf accuracy <
>>> 9.9E-13 Ry
>>>
>>>
>>>
>>>
>>> On Tue, Mar 4, 2014 at 3:06 PM, Sclauzero Gabriele <
>>> gabriele.sclauzero at mat.ethz.ch> wrote:
>>>
>>>> Dear Paresh,
>>>>
>>>> in my understanding you should start with a very small lambda
>>>> value (e.g. 0.1), make sure the calculation has converged (not always
>>>> trivial), then restart with a larger value.
>>>> It is important to tune the steps by which you increase lambda.
>>>> Increasing it by steps of 5 seems too much to me, I would suggest you to
>>>> try much smaller steps, say between 0.1 and 0.5.
>>>>
>>>> There are two reasons why the energy increases: the first is because
>>>> you are constraining your system out of its ground state, but that's
>>>> exactly what one would expect. The other is the contribution from the
>>>> penalty energy (E_constrain, it should be printed after each scf step),
>>>> which is used to impose the constraint.
>>>> An important thing is that this energy term is not physical and becomes
>>>> negligible once your system reaches the target state.Therefore one should
>>>> monitor this constraint energy, together with the constrained quantity, and
>>>> make sure it goes to zero at some point.
>>>>
>>>> Once lambda is large enough and you reached the targeted state,
>>>> E_constrain should be negligible w.r.t. the total energy and of the same
>>>> order of the estimated scf accuracy. From that point on, the energy should
>>>> not change if you further increase lambda, because your system fulfills
>>>> (almost) exactly the constraint, so that E_constrain should stay to a very
>>>> low value.
>>>>
>>>> HTH
>>>>
>>>>
>>>> GS
>>>>
>>>
>>
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://pwscf.org/mailman/listinfo/pw_forum
>>
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140310/6d3f589b/attachment.html>
More information about the users
mailing list