Closed dagewa closed 6 years ago
@cmaxtb Perhaps this was touched on in your earlier paper? I would need to check again. The chicken-and-egg problem would be a theoretical concern if a sample with unknown cell was being analysed and calibration was being done with the diffraction data from that sample alone. However, in practice the distortion map was determined using powder patterns from a known sample, and to date I think we have knowledge of the expected unit cell of the samples that have been analysed by ED. It is true though that these concerns should be addressed as ED moves from niche activity to a tool that might readily be applied to crystals with no prior expectation of the cell and space group
Yes, the distortion map was based on a known aluminium diffraction standard. Calibration of the diffraction setup is something you should ideally always do using something well-known. We could changes the lines below to:
The \emph{datasets 2--7} of our examples all showed a significant elliptical distortion. The parameters of this distortion were determined _using a well known diffraction standar_d as described previously \cite{Clabbers2017}.
We also mention that:
Instruments used for electron diffraction should therefore be well calibrated \cite{gemmi_adt:2015}.
Maybe we can make this statement a bit clearer, or just mention it in the response.
Reply: We have made it clearer that in our case the distortion map was calculated based on an independent, well-known diffraction standard (thus avoiding the "chicken and egg" issue). We also noted that this is good practice and would become essential if ED were being used to analyse a sample of previously unknown unit cell.