If the automated analysis of the dauvergne_protocol.py sample script or the GUI model-free analysis which uses the same protocol has been used, then the following citations are all implicit:
Otherwise, if model-free analysis is used in relax but not via the inbuilt automated protocol, the first reference is for model selection, the second is for eliminating failed model-free models, and the forth is for the optimisation improvements (the third and fifth are for the automated protocol). All of the model-free implementation details of relax are covered by the PhD thesis (available as a PDF or as a printed version on Amazon.com) of:
The reference for the hybridisation of different global diffusion models to analyse the residual inter-domain dynamics - a not very well documented feature of relax - is:
The base citations for model-free theory are Clore et al. (1990); Lipari and Szabo (1982b,a).
The relax user manual (PDF), created 2019-03-08.