[Wien] Using afminput for rutile MnF2

[Peter Blaha]

I suggest you stick to runsp.

When the lattice changes, afminput will not work.

If cpu time is really an issue (I doubt !) one could also find
the "rules" from case.clmvalup/dn after the first scf-cycle.


Am 10.08.2011 22:05, schrieb Cormac McGuinness:
> Dear list,
>
> I thought it would be straightforward to setup an AFM calculation for
> rutile MnF2, but I am clearly misunderstanding the manual and the
> section regarding the afminput.  Clearly I can follow the example in
> Dufek et al (PhysRevB 48, 12672, 1993) and do a spin-polarised
> calculation for MnF2 using a cell of spacegroup Cmmm which is double
> the size of the rutile until cell (spacegroup P42/mnm), and whose
> a-axes are rotated 45 degrees from those of the tetragonal rutile unit
> cell.  However, the local coordinate frames for all the atoms change
> from the rutile unit cell to the Cmmm unit cell, as the global unit
> cell basis it is rotated by 45 degrees. The spin up and down of the
> now inequivalent magnetic ions (the Mn) are specified as input to
> instgen_lapw
>
> Instead of simply doing a spin-polarised calculation, I though I
> should use afminput. Thus I have tried to follow the Wien2k userguide
> and use afminput to set up a symmetry operation to map the spin up
> states onto the spin down states, saving computer time and preserving
> symmetry (as explained in sections 4.5.4 and 9.5). The expectation for
> the symmetry transformation required is a 90 degree rotation about the
> c-axis and a translation of 0.5, 0.5,0.5.
>
> In doing so I have tried to set up the rutile unit cell for MnF2 as a
> case.struct_supergroup in order to let afminput automatically select
> the required symmetry operation and generate the Fourier components
> for the transformation. However when running afminput  I keep getting
> told that the "The super and subgroups are TRANSLATIONENGLEICH" and
> get an identity matrix and a null primitive translation (0 0 0) as the
> symmetry operation.
> There is a specific warning in section 4.5.4 about cases where e.g. y
> and z axes are interchanged at the behest of sgroup. Though this is
> not the case in rutile, both the global coordinate frame is rotated,
> and some of the local coordinate frames are also rotated from the
> P42/mnm unit cell to the Cmmm unit cell. I have tried to heed these
> warnings, but did not understand the exact sequence required (set
> NSYM=0 in the case.struct but not the case.struct_supergroup?/  change
> the local coordinate frames in all cases?)
>
> Alternatively, in the absence of a case.struct_supergroup I have tried
> to specify the rotation and translation directly, but to no avail.
> afminput fails with an error "rrot not found", as no equivalent atom
> is found in the Cmmm spacegroup for the transformation specified.
>
> Finally, in frustration I tried taking the rutile call and converting
> it into a P cell and splitting the Mn (and F) positions, and giving
> the two Mn atoms u and d spins respectively through instgen_lapw.
> Using the non-magnetic rutile cell as the case.struct_supergroup then
> "x afminput" gave me the expected symmetry operation! However it also
> gave me a zero length case.inclmcopy_st file
>
>
> I have not attached anything to this request, as I had generated so
> many struct files (not to mention .inst and .outputeafminput) files
> that I would not want to burden the list with unnecessary attachments.
>
> Should I just stick to the spin-polarised calculation?
>
> Yours
> Cormac
>
> --
> Dr. Cormac McGuinness, Lecturer, School of Physics., Trinity College,
> Dublin, Ireland.
> Phone: +353 1 8963547    Fax: +353 1 6711759    Office: SNIAM 3.17
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien

-- 

                                       P.Blaha
--------------------------------------------------------------------------
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/
--------------------------------------------------------------------------