Convolved peak shape with offset peak position

ChrisRidley

Is it possible to define a custom peak_type pv, where the peak is convolved of two gaussians with a user-specified offset between the two peak centres away from the nominal 'centre'? Something like peak_type pv split. I can do this with single peak fitting easily, but I am looking to do this for all the peaks from a specified crystal structure.

johnsoevans

Almost certainly yes! This is basically similar to e.g. having an emission profile with kalpha1/kalpha2 components for lab data so should be possible. If nothing built-in works you can try a user_defined_convolution.
I don't know what data you're trying to fit (so sorry if the following is patronising): with powder diffraction split peaks often means 2 phases with similar cell parameters, or two different effective sample positions. Would just adding a second str with the same contents but different cell parameters solve your problem? Of if you have a peak position difference that's linear in X you could have two strs with different zero point corrections (or heights). If your peak offsets change with X for different reasons you could write a bespoke "th2_offset = ....;" type equation for one of the strs.

ChrisRidley

Thanks John - I have some TOF neutron data from guide with two distinct primary flight paths - this results in data from a single phase having peakshapes which cannot be accounted for with any number of additional gaussians/lorentzians/exponentials/broadenings modesl, but can be accounted for with an offset additional reflection, which scales linearly with d-spacing/TOF. As you say, this is analagous to alpha1/alpha2 like behaviour, but I have TOF neutron data. Ideally I would treat this with the peakshape rather than multiple strs, so I will play around with the user_defined_convolution