[Pw_forum] how to calculate carbon nanorribon with AFM ordering

[Giovanni Cantele]

On Nov 25, 2013, at 11:49 AM, José Gadelha da Silva Filho <gadelha at fisica.ufc.br> wrote:

> I tried  to calculate DOS for  graphene nanoribbon  with antiferromagnetic (AFM) configuration. I used  QE  4.1.2, QE 5.0 and QE 5.0.2.  Unfortunately I always take a FM ordering.  I would like to know what is wrong in my input data:
> 
> 
> &control
> calculation = 'scf' ,
> outdir = 'fita' ,
> pseudo_dir = 'pseudo' ,
> prefix = 'fita' ,
> verbosity = 'high' ,
> wf_collect=.true.,
> /
> &system
> ibrav=0,
> nat = 10,
> ntyp = 4,
> ecutwfc = 93 ,
> nbnd = 60,
> occupations = 'smearing' ,
> degauss = 0.008 ,
> nspin = 2, 
> starting_magnetization(1) = 1.0,
> starting_magnetization(2) = -1.0,
> starting_magnetization(3) = 1.0,
> starting_magnetization(4) = -1.0,
> /
> &electrons
> diagonalization='david',
> mixing_mode = 'plain',
> mixing_beta = 0.7,
> conv_thr =  1.0d-6,
> /
> ATOMIC_SPECIES
>  H1  1.007940  H.pw-mt_fhi.UPF 
>  C1  12.010700 C.pw-mt_fhi.UPF
>  C2 12.010700 C.pw-mt_fhi.UPF
>  H2 1.007940  H.pw-mt_fhi.UPF
> ATOMIC_POSITIONS crystal
>  H1 0.987129 0.348775 0.499998
>  C1 0.987081 0.389095 0.500002
>  C2 0.487078 0.413829 0.500002
>  C1 0.486874 0.466305 0.500002
>  C2 0.986871 0.491858 0.499998
>  C1 0.986838 0.543986 0.500002
>  C2 0.486787 0.569538 0.500002
>  C1 0.486868 0.622014 0.500002
>  C2 0.986868 0.646743 0.500002
>  H2 0.986685 0.687058 0.499998
> CELL_PARAMETERS bohr
> 4.705211 0.000000 0.000000
> 0.000000 52.410382 0.000000
> 0.000000 0.000000 16.588710
> 
> 
> K_POINTS automatic
> 15 1 1 0 0 0 
> 
> 
> 

Unless some serious bug is introduced in a version, changing QE version is not the
degree of freedom I would investigate firstly!!!  ;-)

If you did not it previously, first check your input file using xcrysden (unfortunately I cannot do it at
the moment because I've been unable to get a working xcrysden version under Mac Os X 10.8.5,
but this is another story!).
However, provided that your input structure is correct, I would not force initial magnetisation an ALL
carbon atoms, also including hydrogens. It is not necessary to impose the initial magnetization on all atoms,
just a small perturbation with respect to the zero-magnetization state is enough, at least in this case.
Therefore, you can try just to set magnetization +0.5 and -0.5 on the two outermost (edge) C atoms, leaving all 
the other atoms (including H's) with no initial guess.

Giovanni


PS maybe you can reduce (to get a faster calculation) the 52 a.u. length of the second lattice vector and use an US
pseudopotential for both H and C, allowing to drastically reduce the ecutwfc value.


--

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Scienze Fisiche
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele
                     http://www.nanomat.unina.it

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