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

sreekar guddeti colonel.sreekar at gmail.com
Thu Aug 25 12:25:30 CEST 2011

```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
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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