[Pw_forum] pwscf: constrained total magnetic moment

[German Samolyuk]

Dear Gabriele,

I do two Fermi level fixed magnetic moment calculation.
There is print in subroutine electrons.f90 version 4.2.1 in line 462
WRITE( stdout, 9072 ) bfield(3),
and bfield(3) is determined as (ef_up-ef_dn)/2.
I gives some estimation for for "equivalent" magnetic field.
I understand that this is very rough estimate.
The question was how to recalulcate it to Tesla.
As I understand, it should be (ef_up-ef_dn)/(2mu_B).

Thanks,

German
ORNL



On Fri, Jan 6, 2012 at 3:26 AM, Gabriele Sclauzero
<gabriele.sclauzero at epfl.ch> wrote:
> Dear German,
>
>    In my previous answer I actually didn't get the point of your question.
> Now I think I've understood better your concern, but some points of your
> message still look obscure to me.
>
> Il giorno 05/gen/2012, alle ore 19.41, German Samolyuk ha scritto:
>
> Dear Gabriele,
>
> Thank you for your answer.
> I use version 4.2.1 and the input I used works for this version. For
> the 4.3.2 vesion the input should be as you mentioned
> tot_magnetization = some_number;. The results obtained with both
> version are the same.
>
>
> What results? Do you mean the same energy? Total magnetization? Both?
>
>
> The output from 4.2.1 version has value of "corresponding" magnetic
> field which according to text is defined as (e_f_up-e_f_dn)/2 in
> Rydbergs.
>
>
> Which text? Where did you find this definition? What is the "corresponding"
> magnetic field?
>
> My question was if there is any way to estimate corresponding external
> magnetic field?
>
>
> If you use the constrained magnetization method, the external magnetic field
> should vanish as you reach the ground state with the target magnetization
> (see the form of the penalty functional here below). This may not happen if
> your value of lambda is too small, because it needs to be large enough to
> make energetically favored the state with the target symmetry. I don't think
> you should attach any physical importance to a nonzero constraining
> field. This said, things can be tricky, because if you increase lambda the
> charge density might become nearly impossible to  converge. If this happens,
> you should try to decrease mixing_beta and/or make a chain of several runs
> where you "restart" from the previous charge density by progressively
> increasing lambda.
>
> If you use the other method in version 4.3.2, there shouldn't be any
> external magnetic field.
>
> HTH
>
> GS
>
>
> Thank you,
>
> German
>
>
> On Thu, Jan 5, 2012 at 5:50 AM, Gabriele Sclauzero
> <gabriele.sclauzero at epfl.ch> wrote:
>
> Dear German,
>
>
>     have you checked the manuals? In the input description of PWscf I've
>
> found:
>
>
>                    'total':
>
>                             total magnetization is constrained by
>
>                             adding a penalty functional to the total energy:
>
>
>                             LAMBDA * SUM_{i} ( magnetization(i) -
>
> fixed_magnetization(i) )**2
>
>
>                             where the sum over i runs over the three
>
> components of
>
>                             the magnetization. Lambda is a real number (see
>
> below).
>
>                             Noncolinear case only. Use "tot_magnetization"
>
> for LSDA
>
>
> I think that, in order to fix the total magnetization in LSDA calculations
>
> (nspin=2), you should simply set the tot_magnetization parameter
>
> (two-Fermi-energies method) and not specify the constrained_magnetization
>
> keyword. Which version of QE are you using?
>
>
>
> HTH
>
>
> GS
>
>
>
> Il giorno 03/gen/2012, alle ore 20.10, German Samolyuk ha scritto:
>
>
> Dear all,
>
>
> I do self-consistent calculation of supercell with 135 Fe atoms with
>
> constrained magnetization.
>
>
> nspin = 2,
>
> fixed_magnetization(3) = 360.0,
>
> constrained_magnetization = 'total' ,
>
>
> The output value of magnetic field:
>
>
>   Magnetic field            =   0.0785401 Ry
>
>
>
> In order to make a rough estimation of corresponding magnetic field in
>
> Tesla I should divide this value by mu_B and difference between
>
> total magnetic moments of system with constrain and without it?
>
>
> Thank you
>
>
> German Samolyuk
>
> Oak Rigde National Laboratory
>
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>
> § Gabriele Sclauzero, EPFL SB ITP CSEA
>
>    PH H2 462, Station 3, CH-1015 Lausanne
>
>
>
>
>
>
>
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>
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> § Gabriele Sclauzero, EPFL SB ITP CSEA
>    PH H2 462, Station 3, CH-1015 Lausanne
>
>
>
>
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