[Pw_forum] halp

[Matteo Cococcioni]

I do not know anything about this compound. I assume you want to
distinguish Cr atoms into two groups to assign them opposite magnetization
(for the AFM case), is this right?
If this is the case you do not have any problem for the FM as all the Cr
can be treated as of the same kind and assigned the same magnetization. In
any case you just need a starting_magnetization (between 0 and 1) for each
kind of Cr different from 0, the value is not very important (it is
re-computed anyway during the calculation). If you read the manual you find
plenty of explanation about this.
In the AFM case you just need to assign half of them spin up and the other
half spin down (positive or negative starting_magnetization, respectively),
after specifying them as of two different kinds (albeit corresponding to
the same pseudopotential, as in the NiO case). Of course, the energy will
probably change depending on which ones you pick as up and downs, but it is
your job to find the ground state magnetic configuration of the system.

hope this helps clarifying your questions.

Please share your name and affiliation.

Matteo



On Tue, Jan 20, 2015 at 7:50 AM, N Bolandhemat <bolandhemat.n at gmail.com>
wrote:

> Dear all
> I am calculating the FM and AFM properties of CdCr2O4 with the 4 atoms of
> Cr in fourteen-atom CdCr2O4 unit cell.In order to run the scf calculation
> for FM in a cubic structure I have a few problems if anyone can help me: 1.
> how can I find the actual number of starting_magnetization? 2. how can I
> identify the different Cr (1 and 2) in the ATOMIC_POSITION as i have 4 Cr?
> (below is the scf code of my compound and fallowing that the NiO magnetic
> example that I am fallowing)
>
> scf code of CdCr204(FM)
> &control
>     calculation='scf'
> /
> &system
>                      ibrav = 2,
>                      celldm(1)= 16.3782,
>                      .
>                      .
>                      nspin=2,
>                      starting_magnetization(1)= ?
>                      starting_magnetization(2)= ?
> /
> &ELECTRONS
>
> /
> CELL_PARAMETERS
>
> ATOMIC_SPECIES
> Cr1  51.9961  Cr.pbe-sp-van.UPF
> Cr2  51.9961  Cr.pbe-sp-van.UPF
> Cd   112.411  Cd.pbe-n-van.UPF
> O    15.9994   O.pbe-van_ak.UPF
> ATOMIC_POSITIONS (crystal)
> Cr ?       0.500000000   0.000000000   0.500000000
> Cr ?       0.000000000   0.500000000   0.500000000
> Cr ?       0.500000000   0.500000000   0.000000000
> Cr ?       0.500000000   0.500000000   0.500000000
> Cd       0.125000000   0.125000000   0.125000000
> Cd       0.875000000   0.875000000   0.875000000
> O        0.731036464   0.731036464   0.731036464
> O        0.268963536   0.268963536   0.693109391
> O        0.268963536   0.693109391   0.268963536
> O        0.693109391   0.268963536   0.268963536
> O        0.731036464   0.306890609   0.731036464
> O        0.306890609   0.731036464   0.731036464
> O        0.268963536   0.268963536   0.268963536
> O        0.731036464   0.731036464   0.306890609
>
> scf code of NiO(FM)
>
> &control
>     pseudo_dir = '../../pseudo',
>     outdir='../../tmp'
>     prefix='nio',
> /
> &system
>     nspin=2,
>     starting_magnetization(2)= 0.5,
>     starting_magnetization(3)=0.5,
> /
> &electrons
> /
> CELL_PARAMETERS
> ATOMIC_SPECIES
> O    1.  O.pbe-rrkjus.UPF
> Ni1  1.  Ni.pbe-nd-rrkjus.UPF
> Ni2  1.  Ni.pbe-nd-rrkjus.UPF
> ATOMIC_POSITIONS crystal
> O  0.25 0.25 0.25
> O  0.75 0.75 0.75
> Ni1 0.0  0.0  0.0
> Ni2 0.5  0.5  0.5
> K_POINTS automatic
> 4 4 4 0 0 0
>
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