[Wien] how to set supercell of Cmmm structure for MnF2

[Peter Blaha]

The "correct" space group is Cmmm, however, this yields rotatated x,y axesm
which is not very convenient.

I don't understand the argument about "supercell" ??

The most convenient procedure is:

i) Start with normal rutile structure.
ii) "Split" the Mn position: For this you would reset the lattice type to
   P (do not specify any space group !)
   Add a non-equivalent atom   Mn2 (at (0.5,0.5,0.5) and
   remove the second Mn1 atom at the first equivalent position.
iii) Run init_lapw.
   Accept the changes suggested by nn (it will also split the O-positions),
   Do NOT accept the changes of sgroup (there is notthing wrong about sgroup,
   it is just less convenient to use this setting).
   Make sure that symmetry finds 8 symops and some local rotation matrices

>     I want to do the AFM calculation for rutile MnF2. In yours paper (PRB,48,pp12672,1993) it means that AFM MnF2 has an orthorhombic unit cell(Cmmm), which is doubled with respect to the rutile unit cell. But userguide tells me that C types not supported in supercell. I don't know how to construct it. Can anyone give me some advice?


>      By the way, i have done LSDA+U and LSDA calculations for simple rutile MnF2. Is it a non-magnetic calculation or a paramagnetic one? And what's the difference between simple calculation and AFM ?

Nobody can know what you did.
Did you say you do a "spin-polarized" calculation (using runsp_lapw) or
non-spinpolarized (run_lapw) ?
Most likely you did a ferromagnetic calculation ???

AFM simply means, that the two Mn atoms are no longer the same (but have
opposite spin). X-ray diffraction is not sensitive to magnetization, thus
MnF2 is found in "rutile" structure when magnetism is not considered.

                                      P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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