[Wien] Help on AFM Structure
Peter Blaha
pblaha at theochem.tuwien.ac.at
Mon Jan 20 09:57:16 CET 2014
So you have 4 non-equivalent Fe and in total 9 Fe atoms in the cell.
If you don't know anything about magnetism:
1) do it ferromagnetic
2) try out various ferri-magnetic situations (like 1-3=up, 4=dn; but
also others). Compare total energies. Of course with 9 Fe atoms you
cannot generate a perfect antiferromagnet.
Once this is done, you could go to a P-cell (doubling the number of
atoms as done before), but keep the original Fe atoms all up, and only
the new positions (eg. 1: 0,0,0 --> .5,0,.5) all dn. (Still, you would
have only 8 different Fe positions).
On 01/20/2014 09:44 AM, Chinedu Ekuma wrote:
> Dear Peter,
> Thanks for the explanations. There were four inequivalent Fe positions
> in the original structure. Kindly see as attached the original
> structure. I am a bit confused when you said that I should first play
> with the magnetic structure in the first symmetry. What happens to the
> multiplicity?
>
> Best.
> *Ekuma
> *
> /
> /
> ////
>
>
> On Monday, January 20, 2014 3:32 AM, Peter Blaha
> <pblaha at theochem.tuwien.ac.at> wrote:
> This is the wrong strategy. I expected that it is C-centered.
>
> How many Fe positions do you have in CXZ ?
> Try to play with the magnetic configurations in this symmetry first.
>
> Eventually you could give up the C-centering and make the formerly
> centered-atoms antiferromagnetic to the other ones.
>
> Try to visualize the magnetic structures as I told you before. If the
> magnetism is not know from experiment, you have to make "computer
> experiments", but start with the MOST simple possibilities and then
> gradually test more complicated ones.
>
> On 01/20/2014 09:24 AM, Chinedu Ekuma wrote:
> > Dear Peter,
> > The original structure was a CXZ structure but for the AFM calculations,
> > I made all the multiplicity to be 1 and then after that, running x
> > sgroup lead to the reduction in the symmetry.
> >
> > *Ekuma
> > *
> > /
> > /
> > ////
> >
> >
> > On Monday, January 20, 2014 3:19 AM, Peter Blaha
> > <pblaha at theochem.tuwien.ac.at <mailto:pblaha at theochem.tuwien.ac.at>>
> wrote:
> > From where did you get the structure ?? It is really P1 ??
> >
> > Did you remove the the 1,2,3,.. from Fe1, Fe2,..Ga1,Ga2,... ???
> >
> > Maybe there is some rounding error in the positions which prevents
> > higher symmetry ??
> >
> > On 01/20/2014 08:55 AM, Chinedu Ekuma wrote:
> > > Dear Peter,
> > > The structure is the default structure as obtained from running x
> sgroup.
> > >
> > > Best.
> > >
> > > *C. Ekuma*
> > > /
> > > /
> > > ////
> > >
> > >
> > > On Monday, January 20, 2014 2:27 AM, Peter Blaha
> > > <pblaha at theochem.tuwien.ac.at
> <mailto:pblaha at theochem.tuwien.ac.at>
> <mailto:pblaha at theochem.tuwien.ac.at <mailto:pblaha at theochem.tuwien.ac.at>>>
> > wrote:
> > > Is there a reason why you did setup this case in P1 symmetry ???
> > >
> > > You seem to have Fe18 Ga24, which is the same as Fe3 Ga4
> > >
> > > What happens when you remove all "labels" (1,2,3,... 24) of the
> atoms ?
> > > Wien2k will then find out which atoms are equivalent and which are
> > > different by symmetry.
> > > Maybe this is even a C-centered monoclinic structure ?
> > >
> > > Anyway, when you have a structure which has only a "few" (2-4)
> > > nonequivalent Fe positions, then it makes sense to play with magnetic
> > > order and compare total energies.
> > >
> > > You would start in different directories and BEFORE init_lapw run
> > > instgen_lapw -ask and specify the desired magnetic order by chosing up
> > > or dn for each Fe site (and nm for Ga).
> > >
> > > For visualisation you may create a struct file where you rename your
> > > atoms to Co, Ni,...., so that you can distinguish them in xcrysden and
> > > then you can see how to arrange the magnetic moments to get them in a
> > > specific order.
> > >
> > >
> > > On 01/19/2014 01:41 AM, Chinedu Ekuma wrote:
> > > > Dear All,
> > > > I am trying to construct a collinear AFM structure from the
> attached
> > > > file. Please, any help will be greatly appreciated.
> > > >
> > > > Thanks.
> > > > *C. Ekuma*
> > >
> > > >
> > > >
> > > >
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> > > --
> > >
> > > P.Blaha
> > >
> >
> --------------------------------------------------------------------------
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> > P.Blaha
> >
> --------------------------------------------------------------------------
> > Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> > Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
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>
> P.Blaha
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
> Email: blaha at theochem.tuwien.ac.at <mailto:blaha at theochem.tuwien.ac.at>
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--
P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at WWW:
http://info.tuwien.ac.at/theochem/
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