[Pw_forum] inequivalent atoms of the same type
Xunlei Ding
ding at sissa.it
Wed Mar 14 09:03:54 CET 2007
Dear Yu,
The "same" atom at different symmetry sites is just the same at initial
time.
When scf calculation is done, they can be totally different.
When we set ntype=2 for the same kind (chemically) of atoms, usually in
magnetic calculation,
we just set different initial parameters for them, such as
starting_magnetization(i), to make the initial state close to the final
result.
For example, we do a calculation on a meterial X (only one kine of atom
X, with two different symmetry site X1, X2).
If the final spin state is X1: 0.5, X2:0.3, then you can set them as the
same atom and just set starting_magnetization(1)=0.7,
and also, you can set them as two kind of atoms, and set
starting_magnetization(1)=0.7, starting_magnetization(2)=0.9.
If the final spin state is X1: 0.5, X2:-0.3, then I think we must set
them as two kind of atoms, and set starting_magnetization(1)=0.7,
starting_magnetization(2)=-0.6.
Hope what I said is right.
Best,
Ding
W. YU wrote:
>Dear PW users,
>
>I have a question concerning the "ntype" keyword:
>
>In a non-magnetic case, if I have the same kind
>(chemically) of atoms which occupy different symmetry
>sites, say "4c" and "4e",and I made them belong to the
>same "type", how will the code find the symmetry for
>these two inequivalent kinds of atoms. If it cannot
>differentiate between these two symmetry sites, will
>this has some effect on the results?
>
>Furthermore, in a phonon calculation, the phonon modes
>are associated with different site symmetries. If the
>two atoms in different symmetry sites were treated as
>one kind, will the phonon modes be different?
>
>I would appreciate it if anybody could explain this.
>
>Wen Yu
>
>
>
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