Hi Abdul, In my opinion, the short answer is that your model is wrong; amplitude, coordination number and sigma square are strongly correlated; if your model is not adequate or if values are too far from the convergence zone, non physical effects appear; usually, very small or negative values for sigma2 mean coordination number too low, but very small amplitude means the reverse! I suggest to start with a plain simulation (all parameters locked to expected values) and check that there is not something weird in different k zones, which might eventually indicate unexpected species close to the central atom; my 2 cents, Pierre Le 28/05/2018 à 19:00, ifeffit-request@millenia.cars.aps.anl.gov a écrit :

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Today's Topics:

1. Amplitude and sigma square (Abdul Ahad)

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Message: 1 Date: Mon, 28 May 2018 14:16:39 +0530 From: Abdul Ahad To: ifeffit@millenia.cars.aps.anl.gov Subject: [Ifeffit] Amplitude and sigma square Message-ID: Content-Type: text/plain; charset="utf-8"

Hi all,

I have couple of questions. 1. I found in many tutorials that the value of amp should lie between 0.7 and 1. But when I refined it goes to 0.15, what's wrong with it.

2. The value of sigma2. Some time at high k, value, it turns to negative but small. What I suppose to do?

3. If I need to know the behavior of octahedra distortion with temperature, and it is lies within the first shell. So what is the need of higher shell fitting.???

Thanks in advance