From:
ifeffit-bounces@millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Tadej Rojac
Sent: Thursday, December 15, 2005
6:44 AM
To:
Ifeffit@millenia.cars.aps.anl.gov
Subject: [Ifeffit] my problem
my name is Tadej Rojac and I'm writing from the Institute
Jozef Stefan in Ljubljana, Slovenia. I work in the Department
of electronic ceramics. Actually, I'm working on a EXAFS spectra with Artemis.
What I am trying to do is mainly to describe an EXAFS spectrum with a model
concerning the structure of Nb2O5. I'm working togheter with prof. Iztok Arcon,
who is a specialist in the field. My main problem is that I have to do some
suppositions. In fact Nb2O5 structure is quite complicated. It is composed of
seven different Nb positions which I took into account using 7 feffs in
Artemis. I don't know the exact occupancies of the seven
positions. In order to make the search easier I did at first
a supposition that all the occupancies must be positive, which is
realistic. I set this with the command "abs" in each feff file.
Secondly, I need to supose that the sum of all occupancies is 1. In that
way the search for the result is much easier, otherwise I get the sum greater
than one, which, for sure, is not the case. My question is how can I do that?
For example, if the occupancies are O1, O2, O3, O4, O5, O6 and O7 and I define
them with a starting value (let use say the same, so 1/7) than I can do O =
O1+O2+O3+O4+O5+O6+O7. Finally I need to do O =1, but here Artemis doesn't
want to define the same parameter (O in this case) twice. So, how can I insert
the conditions, that the sum of all the occupancies is 1, into Artemis? I
hope you can help me.
[Kelly, Shelly D.]
In the path page for each path of each feff calculation you
need to have a variable that represents the occupancy.
S02xN = abs(S02 * O1)
…..
Then in the variable page (guess set def)
Guess O1 = 0.15
Guess O2 = 0.15
Guess O3 = 0.15
….
Def O7 = 1 – abs(O1) –abs(O2) –abs(O3) –
abs(O4) – abs(O5) –abs(O6)
Hence you get one occupancy for free for knowing one more
piece of information.
Sounds like a tough problem.
I'm looking forward t hearing from you...thank
you...
Tadej Rojac
Jozef Stefan Institute
Jamova 39
1000 Ljubljana
Slovenia
Tel.: +386 1 477 38 34
Fax: +386 1 477 38 87
E-mail: tadej.rojac@ijs.si