[Wien] How to creat the structure of AgSbTe2?

[Michael Fischer]

Hi,

as far as I understand it, you want to deal with a statistical 
distribution of Ag and Sb over the (0,0,0) position of the rock-salt 
structure. To my knowledge, such a statistical distribution cannot be 
simulated directly using the WIEN-code, as you cannot introduce atoms 
with fractional occupancies in your structure.
However, L.D. Marks suggested an approach that might be applicable for 
your problem, too, in an older thread in the mailing list. I have 
attached it below.

Greetings
Michael

L. D. Marks  L-marks at northwestern.edu
Wed Aug 11 13:30:57 CEST 2004

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This is a rather fundamental problem. In x-ray (electron, neutron)
diffraction when only the Bragg spots are measured, this corresponds to 
a
statistical average structure which can be modelled by partial 
occupancies
of certain sites. There may be long- or short-range ordering of these
sites, which would appear at non-Bragg locations (diffuse scattering).

To model this, you would have to try and construct a supercell with some
appropriate random distribution of the sites, and (rigorously) average
over several supercells with different configurations. There might be 
some
approximations that others could suggest, but I believe that this is a
non-trivial problem without a simple solution (unlike a calculation of a
simple fcc or bcc material).

On Tue, 10 Aug 2004, yanming Ma wrote:

 > Dear Yushan,
 >
 > Thanks for your reply. I understand what you
 > addressed. Actually, I clearly know the real structure
 > for Mo2N. It has pm-3m space group. My problem is how
 > to locate the N atom in the Mo2N.
 > The initial structure for Mo is BCC, the N atoms are
 > doped into the intersitial site of Mo. The thing is N
 > only located in one intersitial site inside one plane
 > of Mo. Another intersitial site inside the plane is
 > vacant. But according to the symmetry operation, there
 > should be a N atom in this site. I was puzzled.
 >
 > Can anybody help me out?
 >
 > Thanks
 >
 > Yanming
 >
 >
 > --- Yushan Wang <wys at UDel.Edu> wrote:
 >
 > > hi, guy,
 > > please read the following phrase:
 > >
 > > A partially disordered structure has been proposed
 > > for gamma-Mo2N on
 > > electron diffraction data. its cubic pattern
 > > cooresponds to a bimolecular
 > > cell, having a0 = 4.165 (anst.).
 > > The four Mo atoms are considered to be in a
 > > face-centered array: 0,0,0;
 > > F.C., with some of the face-centering positions
 > > empty to correspond to a
 > > certain departure from the stoichiometric
 > > composition. One nitrogen atom
 > > is said to be in 1/2, 1/2, 1/2, the other
 > > statistically distributed over
 > > the positions 0,0,1/2; 0,1/2,0; and 1/2,0,0.
 > >
 > >
 > > good luck.
 > >
 > > yushan
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