Hello! First, apologies if the scope of the question is beyond that of the listserv - I was recommended this discussion page through a colleague.
I am incredibly new to refinement, and have been trying to employ the use of Rietveld refinement to better determine the crystal structure of my lead sulfide (PbS) quantum dots. Data was acquired as images on a home-built tabletop time-resolved electron diffraction setup, and converted to diffractogram through a combination of center finding and background subtraction. However, since these are small (~ 5 nm), and we are certainly sampling the ensemble average (as our focused beam is about 120 um in diameter), our pattern is that of a polycrystalline sample. From what I've encountered in my research, Rietveld is best suited for this case. I have taken an initial structure as inferred from literature/the bulk and refined that (relatively successfully to a Rwp value of ~2 - 6%). I do have a few questions regarding this process as I believe I am not being as rigorous as possible: - is there a 'best practices' order of refinement operations? e.g. refine the lattice parameters first, then peak profiles, etc. - there is a single peak that is not matching (likely due to a slight deviation in atomic positions from the expected simple cubic structure) - is refinement capable of moving individual atoms or clusters of atoms to better match a small, unaccounted for reflection? For what it's worth, I have been using Reflex in Materials Studio; if there is a more appropriate software for this application, I would be happy to hear! If any additional clarification is need, I'll fill it in! Best, Kamil ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/
