How does x-ray diffraction from different Bragg planes add u

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JacobMarley
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Joined: 20 Aug 2014, 22:52

How does x-ray diffraction from different Bragg planes add u

Post by JacobMarley » 22 Aug 2014, 19:29

I'm writing a little bit of Mathematica code that should be able to make a reasonable powder diffraction spectrum. The algorithm is like this:
[*]Take Bravais lattice and basis. Compute reciprocal vectors.
[*]Compute structure factor (and its square magnitude)
[*]Have triple nested loop that creates ordered triplets of Miller indices. {(h1,k1,l1),(h2,k2,l2)....}
[*]For each of these triplets, compute the momentum transfer vector Q.
[*]Compute the angle of the peak from Bragg's law and the intensity from the structure factor's square.

OK, this algorithm runs. I look through the list of angles. They all compare perfectly with reference literature. Here's where the real question comes in. I have this list of Miller indices, and each one comes with an angle and an intensity. Often, many many many miller indices come at the same Bragg angle, because the MAGNITUDE of Q is the same. Should I just add the intensity (structure factor squared) of these so that they make a superpeak at that angle? Was I wrong to square the structure factor in the first place? Should I instead leave it unsquared and then square it only after I've added together all of the structure factors at a given angle? I tried both of these things, and they both yield nonsense in terms of peak intensity.
The problem is that I'm getting anomalously high peaks at high angle. The atomic form factor should be preventing that from happening. Any insight on this would be greatly appreciated. I can post the code if anyone is interested. It's not that complicated, but I know that reading someone else's code is a drudge

PS: Debye-Waller factor is not the answer. I'm not at high enough momentum transfer for that to account for the massive discrepancies I see.

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