Extending the list of models given in Orekhov et al. (1999a); Korzhnev et al. (2001); Fushman et al. (1997); Mandel et al. (1995); Zhuravleva et al. (2004), the models built into relax include

The parameter *R*_{ex} is scaled quadratically with field strength in these models as it is assumed to be fast.
In the set theory notation, the model-free model for the spin system *i* is represented by the symbol
.
Through the addition of the local *τ*_{m} to each of these models, only the component of Brownian rotational diffusion experienced by the spin system is probed.
These models, represented in set notation by the symbol
, are

The relax user manual (PDF), created 2020-08-26.