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TeixeiraWater

Description

Teixeira’s model for water [1].

Models the Q dependence of the QENS line width (Gamma (hwhm)), diffusion coefficients (D), residence times (tau) and jump lengths (length) to extract the associated long range diffusive motions of molecules.

This model (1961) has the form:

\[ \begin{align}\begin{aligned}HWHM(Q) = \frac{\hbar}{\tau} \cdot \frac{(QL)^2}{6 + (QL)^2}\\D = \frac{L^2}{6 \tau}\end{aligned}\end{align} \]

Units of \(L\) are inverse units of \(Q\).

Units of \(HWHM\) are \(meV\) if units of \(\tau\) are ps. Alternatively, units of \(HWHM\) are \(\mu eV\) if units of \(\tau\) are ns.

Properties (fitting parameters)

Name	Default	Description
Tau	1.0	Residence time
L	1.5	Jump length

References

[1]

10. Teixeira, M.-C. Bellissent-Funel, S. H. Chen, and A. J. Dianoux. Phys. Rev. A, 31:1913–1917

Categories: FitFunctions | QuasiElastic

Source

Python: TeixeiraWater.py