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

[Gabriele Sclauzero]

Dear Sreekar,

I would first try to reduce mixing_beta  and also lambda (say, to 0.2 or 0.1). You can then restart the calculation with a larger value of lambda.

Don't forget that for USPP you need to specify also ecutrho, and perhaps you don't need such a high ecutwfc.
If your USPPs are those on the QE website, I would use ecutwfc=35 and ecutrho=350, for instance.



Il giorno 25/ago/2011, alle ore 12.25, sreekar guddeti ha scritto:

> 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"

Indeed this looks suspicious... one should look into the code to understand what's going on. You can have a look into add_bfield.f90, it should not be very difficult to understand how it works.

Good luck


GS


> 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
> 
> <grapheneznrn10j.scf.in>_______________________________________________
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§ Gabriele Sclauzero, EPFL SB ITP CSEA
   PH H2 462, Station 3, CH-1015 Lausanne







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