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Re: [sdpd] atom occupation in fullprof examples

Hello,

According to the Fullprof  manual:

Occ - Occupation number:
Occupation number i.e. chemical occupancy × site multiplicity (can be 
normalised to the multiplicity of the general position of the group).

Thus this parameter takes account of the site multiplicity and not only 
of the chemical occupy.

For instance in the exemple that you quote:
Si3N4 - SG: P 3 1 c

Si1  site:6c (number of positions:6)
Si2  site:6c
N1  site:6c
N2  site:6c
N3  site:2b
N4  site:2a

So for a full occupancy of the sites: occ in fullprof will be
6 for Si1, Si2, N1, N2
2 for N3 and N4

And if you normalize to the multiplicity of the general position of the 
group (6) (il is often advised to normalize so that ATZ corresponds to 
the relative mass of a unit cell).
1 for Si1, Si2, N1, N2
1/3 for N3 and N4

Patrick Weisbecker

PS: for iron (BCC) site 2a give a occ number of  2/96=0.02083 for a full 
occupancy.

Hamid Mutaalim a écrit :

Dear all,
I have some questions about atoms occupation in some
example found with Fullprof program (November04):

1-In tbbaco.pcr file
The formula of the compound is Tb2BaCoO5 but in atoms
refinements the occ. given are
Ba--0.125
Tb--0.250
Co--0.125
O1--0.5
O2--0.125

> From these cccupations values and Wyckoff sites

multiplicity , I found different formula from the
above formula.Is it correct? any explanation

2-In some example the occupation is 0.00238, it is
very near to zero: is there any meaning for this value

3- In Si3N4r.pcr file, we have the following occ.
values:
Si1--3.00
Si2--3.00
N1--3.00
N2--3.00
I am thinking that the occupation value must be always
between 0 and 1. How to explain this.

Thank you for your informations
Hamid

 


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