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DiffRotDiscreteCircle¶
Description¶
Summary¶
This fitting function models the dynamics structure factor of a particle undergoing discrete jumps on N-sites evenly distributed in a circle. The particle can only jump to neighboring sites. This is the most common type of discrete rotational diffusion in a circle.
Markov model for jumps between neighboring sites:
The Decay fitting parameter \(\tau\) is the inverse of the transition rate. This, along with the circle radius \(r\), conform the two fundamental fitting parameters of the structure factor \(S(Q,E)\):
The transition rate, expressed in units of energy is \(h\tau^{-1}\), with h = 4.135665616 meV ps.
This function is a composite of ElasticDiffRotDiscreteCircle and InelasticDiffRotDiscreteCircle.
When using DiffRotDiscreteCircle, the value of Q can be obtained either though the Q attribute or can be calculated from the input workspace using the WorkspaceIndex property. The value calculated using the workspace is used whenever the Q attribute is empty.
Example: Methyl Rotations¶
Methyl Rotations can be modelled setting N=3. In this case, the inelastic part reduces to a single Lorentzian:
If, alternatively, one models these dynamics using the Lorentzian function provided in Mantid:
Then:
Attributes (non-fitting parameters)¶
Name |
Type |
Default |
Description |
---|---|---|---|
N |
|||
NumDeriv |
|||
Q |
|||
f0.N |
|||
f0.Q |
|||
f0.WorkspaceIndex |
|||
f1.N |
|||
f1.Q |
|||
f1.WorkspaceIndex |
\(N\) (integer, default=3) number of sites - \(NumDeriv\) (boolean, default=true) carry out numerical derivative - \(Q\) (double, default=0.5) Momentum transfer .. properties:
.. categories::
Source¶
C++ header: DiffRotDiscreteCircle.h
C++ source: DiffRotDiscreteCircle.cpp