[Wien] Partial Occupancy problem

[Siew Wei Goh]

Dear Prof Blaha and Wien users

 

Happy New Year!

 

I am trying to simulate S K-edge NEXAFS spectra on pentlandite (Fe,Ni)9S8.
I am having major problem with simulating this structure because of the
partial occupancy of its Ni and Fe atoms!  I have been searching for
possible guide in how to deal with partial occupancy in WIEN2k from the User
Forum. There had been a few entries on Partial Occupancy and I followed the
link through, but still found no solution to my problem.  In the forum, it
says to "try combination of sites"!  In my attempted to do this, I could not
get WIEN to run my modified structures.  I will describe below what I had
attempted.

 

I thought to simplify the calculation by attempting to calculate for
Fe5Ni4S8.  First I generated the pentlandite structure by using only Fe
atoms on both the metal sites, octahedral and tetrahedral sites (see
attached structure file, "Pn_Fe.struct"). This gives 48 symmetry.

 

Next I took out 4 of the 8 atoms from the Fe tetrahedral sites {ATOM -2} and
put Ni atoms into those coordinate.  I then change the ATOMS number
accordingly (see attached "Pn_FeNi edited.struct".  When attempting to run
WIEN on this modified structure without running pass StructGen session, it
tells me that I've got the wrong inequivalent atoms and asked me to select
the suggested space group - this would change the cubic structure (space
group 225) into tetragonal (space group 216)! See attached "Pn1.struct".  I
do not think simulations obtained from this alternative suggested space
group is appropriate to describe pentlandite!  It would have altered the
positions or the atoms itself and so the absorption spectra would also be
affected! Am I right?

 

If I forced WIEN to continue without changing the space group, it soon ran
into SYMMETRY problem during initialization stage!  

 

I'd also tried running the modified structure pass StrucGen first.  However,
this doesn't help because it simply generate identical multiplicity metal
coordinates for both the Fe and Ni atoms!  And. WIEN ran into error!

 

Obviously I had been going about the wrong way in getting WIEN to work on
this structure.  Please advice what can I do to get WIEN to run the
structure with the correct space group.  Many thanks in advance.  Once
again, Happy New Year!

 

 

Fm3m  225

a = 10.03 Angstrom

alpha = 90 deg

 

atom                 x          y          z                      occupancy

Fe (Oct)            0.5        0.5        0.5                    1.0

Fe (Tet)             0.125    0.125    0.125                0.5

Ni (Tet)             0.125    0.125    0.125                0.5

S 1                    0.25      0.25      0.25                  1.0

S2                     0.25      0          0                      1.0

 

 

Regards,

 

Siew Wei Goh

School of Chemistry

University of New South Wales

Sydney NSW 2052, Australia

Tel: +61 (2) 9385 5519

 

 

 

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