The LM63 2-site fast exchange CPMG model

This is the original model for 2-site fast exchange for CPMG-type experiments.
It is selected by setting the model to `LM63', here named after Luz and Meiboom (1963).
The original *n*-site Equation (7) from their paper can be written as

R_{ex} = 1 - 2τ_{ex}g⋅tanh2τ_{ex}g⋅τ_{ex}⋅p_{i}Δω_{i}, |
(11.14) |

where *g* is the pulse repetition rate defined as

g = 2ν_{CPMG}. |
(11.15) |

It can be rearranged as

The equation for the 2-site exchange process can be expressed as

R_{2eff} = R_{2}^{0} + ⋅1 - ⋅tanh. |
(11.17) |

The reference for this equation is:

More information about the LM63 model is available from:

- the relax wiki at http://wiki.nmr-relax.com/LM63,
- the API documentation at http://www.nmr-relax.com/api/3.2/lib.dispersion.lm63-module.html,
- the relaxation dispersion page of the relax website at http://www.nmr-relax.com/analyses/relaxation_dispersion.html#LM63.

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