I have a question regarding the calculation of coordination numbers from PDF data. I browsed several similar topics here on the Google group but none of them seems to address my issue.
I am currently working with PDF data of metal-oxide nanoparticles, but for educational purposes I decided to start off with a simpler example of Ni data from cmi_scripts
and already encountered some problems.
As I can understand from the literature (e.g. Underneath the Bragg Peaks), to calculate the coordination numbers I first need to calculate a Pair Correlation Function g(r) from my PDF using the formula g(r) = G(r)/(4πr×ρ0) + 1. At the same time, the term -4πr×ρ0 should act as a sloped baseline for my G(r). I understand ρ0 as a mean electron density per 1 Å3, so for Ni, I calculated it as (28e × 4 atoms per unit cell)/43.76 Å3 = 2.56 e/Å3. However, this results in the slope of -4πr×ρ0 being too far off of what it is expected to be (plot attached). Nevertheless, for the sake of getting a sane g(r) and also doubting the correctness of my ρ0 calculation, I decided to multiply the -4πr×ρ0 term by some coefficient to make the slope look correct (plot attached), and this turned out to be 3×10-2. Then I calculated g(r) = G(r)/(4πr×2.56×3×10-2) + 1 and it looks great in contrast to what I got by simply doing g(r) = G(r)/(4πr×2.56) + 1. But integrating the first two peaks I get the numbers that are way off, not only in terms of the absolute values of the integrals but also in terms of their ratio (plot attached).
So I would be happy if anyone points out where my approach is flawed and how should I adjust my calculations to get the correct values at least for this example dataset and then move forward to my metal-oxide nanoparticles.
Any hints are appreciated.