The parameters of the Brownian rotational diffusion tensor belong to the set . This set is the union of the geometric parameters and the orientational parameters ,

(15.4) |

When diffusion is spherical solely the geometric parameter
is optimised.
When the molecule diffuses as a spheroid the geometric parameters
and
and the orientational parameters *θ* (the polar angle) and *φ* (the azimuthal angle) are optimised.
If the molecule diffuses as an ellipsoid the geometric parameters
,
, and
are optimised together with the Euler angles *α*, *β*, and *γ*.

This category is defined as the optimisation of solely the parameters of . The model-free parameters of are held constant. As all selected residues of the macromolecule are involved in the optimisation, this category is global and can be more complex than the optimisation of or . The dimensionality of the problem nevertheless low with

dim | (15.5) |

for the diffusion as a sphere, spheroid, and ellipsoid respectively.

The relax user manual (PDF), created 2019-03-08.