[Ifeffit] pi/2deltak

[Avakyan L.A.]

Hello Riti,

the criterion of R-resolution of pi/2deltak can be drawn from the 
Nyquist theorem.
The amount of information in the spectra is limited by Nidp = 2 deltak 
deltaR / pi.
Then, in assumption of equal distribution of information over the 
R-interval, the minimal interval can be estimated as deltaR / Nidp = 
pi/2deltak.
The problem is that exact formula for Nidp is not known. Sometimes it 
has addition of +1 or +2 to represent the fact that single point 
(deltak=0) still contains information.
Moreover, information is not equally distributed: some k-regions are 
more rich, other are less...

And when energy interval is very short (glass, liquid) this question 
becomes vital. Sometimes, this resolution limit can even be overcome as 
it is shown in [http://dx.doi.org/10.1103/PhysRevB.82.064204].

Best regards,
Leon

Leon Avakyan
PhDr, Physics Faculty,
Southern Federal University
laavakyan at sfedu.ru


On 31.01.2016 21:00, ifeffit-request at millenia.cars.aps.anl.gov wrote:
> Message: 2
> Date: Sat, 30 Jan 2016 17:35:04 -0800
> From: Ritimukta Sarangi<ritimukta at gmail.com>
> To: XAFS Analysis using Ifeffit<ifeffit at millenia.cars.aps.anl.gov>
> Subject: [Ifeffit] pi/2deltak
> Message-ID:
> 	<CAMWiF7ymrKEDSZw31pcgwCzZH5tsFvFk+151gxfjRz9jUARH4w at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hello,
>
> I was recently asked about the accuracy of this formulation for obtaining
> EXAFS resolution and I did not have a good answer. Can someone point to a
> reference or explain here?
> Thank you for your time,
> Best,
> -Riti