[Ifeffit] Scanning of "Potential Surfaces" in EXAFS

Norbert Weiher weiher at tech.chem.ethz.ch
Tue Jul 8 06:24:52 CDT 2003

Hi folks,

first of all thanks to all of you who attended the XAFS XII for an interesting 
conference with lots of input and new ideas.

But now to my question:

I have been guessing for a long time of doing an algorithm of doing some kind 
of potential surface scanning when doing an EXAFS fit. This procedure has 
been known in e.g. ab initio codes like GAUSSIAN for a long time and can be 
used to check if you are really in a global minimum on the potential surface. 
As EXAFS analysis is the ultimate search for a global minimum in the 
parameter space, but you never know if you really end up there, I was 
planning to do such kind of investigations.

However, before I start off with wild coding :) I want to have more opinions 
on this topic. Here are my main points speaking for this kind of algorithm:

1) Computer power is quite fast now - and ifeffit is also really fast in 
computing the fit quality if you do not guess any variable (which you don't 
need in this case as you vary the parameters by your own).

2) In cases where you would expect large correlations between certain 
variables (e.g. when you have overlapping shells at nearly the same 
distance), one could systematically investigate the influence of small 
changes in the parameter space on the fit.

That's it - now I am really keen on knowing what you think of this idea. 


Dr. rer. nat. Norbert Weiher (norbertweiher at yahoo.de)
Laboratory for Technical Chemistry - ETH Hönggerberg
HCI E 117 - 8093 Zürich - Phone: +41 1 63 3 48 32

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