[Pw_forum] constrained magnetization calculation to converge at the ferromagnetic state

[Arles V. Gil Rebaza]

Dear Sreekar Guddeti, if you want to calculate a constrained magnetization
with antiparallel direction between the atom 2 and atom 8, you must to put
the "starting_magnetization" tag with opposite value, for example:

  starting_magnetization(2)=  0.3091,
  starting_magnetization(8)= -0.3091,

best wishes

PhD stud. Arles V. Gil Rebaza
Instituto de Física de La Plata
Argentina.

2011/8/25 sreekar guddeti <colonel.sreekar at gmail.com>

> Respected Sir/Madam,
> 1. I would like to perform a constrained magnetization calculation for a
> system, whose unconstrained spin polarized calculation gives an
> antiferromagnetic state, to converge at the ferromagnetic state.
> 2. The system is a zigzag graphene nanoribbon(*
> http://en.wikipedia.org/wiki/Graphene***) and I would like to flip the
> atomic moment at one of the edge site and constrain both the edge site
> moments.
> 3. I calculated the antiferromagnetic edge site moment  using PDOS
> calculation. I used 'lambda' parameter to constrain the moments.
>
> 4.Questions: Is 3) the right way to do it? If yes, what should be value of
> lambda? I used lambda =1 and the scf output (given below) is disturbing... I
> would like to ask what does "constrained moment :   -20.000000" mean and why
> is the constrain energy so high.  If it is not the right way, I would be
> grateful if you could suggest an alternative.
>
> Thanking you,
> Yours sincerely,
> Sreekar Guddeti
> Undergraduate (5th year)
> Engineering Physics
> IIT Bombay
> India
>
> PS: The system namelist for scf calculation and the sample output are given
> below and the complete input file is attached.
>
>
> --------------------------------------
> ...
>
>  ==============================================================================
>      atom number   15 relative position :   -3.5000   6.0622   0.0000
>      charge :     0.983302
>      magnetization :          0.000256
>      magnetization/charge:    0.000260
>      constrained moment :     0.309100
>
>
>  ==============================================================================
>
>
>  ==============================================================================
>      atom number   16 relative position :   -3.0000   5.7735   0.0000
>      charge :     1.783674
>      magnetization :         -0.385046
>      magnetization/charge:   -0.215873
>      constrained moment :   -20.000000
>
>
>  ==============================================================================
> ...
> ...
>
> *constraint energy* (Ryd) =   6095.83663339
> ---------------------------------
>
>
>
> --------------------------------
> &SYSTEM
>                        ibrav = 12,
>                    celldm(1) = 4.608737,
>                    celldm(2) = 12.0,
>                    celldm(3) = 10.0,
>                    celldm(4) = -0.50,
>                          nat = 18,
>                         ntyp =10,
>     starting_magnetization(2)= 0.3091,
>     starting_magnetization(8)= 0.3091,
>                   occupations='smearing',
>                      smearing='gauss',
>                       degauss=0.01,
>                         nspin=2,
>     constrained_magnetization='atomic'
>                       lambda = 1
>                      ecutwfc = 50.D0 ,
>                       report = 2
>
>  /
>
>
> --
> Sreekar Guddeti
>
>
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>
>


-- 
###--------->   Arles V.   <---------###
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