This fitting function models the dynamics structure factor of a particle undergoing continuous diffusion but confined to a spherical volume. According to Volino and Dianoux 1,
Because of the spherical symmetry of the problem, the structure factor
is expressed in terms of the
spherical Bessel functions.
Furthermore, the requirement that no particle flux can escape the sphere
leads to the following boundary
condition2:
The roots of this set of equations are the numerical coefficients
.
The fit function DiffSphere has an elastic part modeled by fitting function ElasticDiffSphere, and an inelastic part modeled by InelasticDiffSphere.
Name | Type | Default | Description |
---|---|---|---|
NumDeriv | |||
Q |
(boolean, default=true) carry out numerical derivative -
(double, default=1.0) Momentum transfer
Name | Default | Description |
---|---|---|
f0.Height | 1.0 | Scaling factor to be applied to the resolution. |
f0.Centre | 0.0 | Shift along the x-axis to be applied to the resolution. |
f0.Radius | 2.0 | Sphere radius |
Intensity | 1.0 | scaling factor |
Radius | 2.0 | Sphere radius, in Angstroms |
Diffusion | 0.05 | Diffusion coefficient, in units of A^2*THz, if energy in meV, or A^2*PHz if energy in ueV |
Shift | 0.0 | Shift in domain |
Categories: FitFunctions | QuasiElastic
C++ source: DiffSphere.cpp (last modified: 2018-10-05)
C++ header: DiffSphere.h (last modified: 2018-10-05)