Intermediate scattering function¶

The module computes the intermediate scattering function

$S_{(\alpha\beta)}(\vec k, t) = \frac{1}{N} \bigl\langle \rho_\alpha(\vec k, t)^* \rho_\beta(\vec k, 0) \bigr\rangle$

from the Fourier modes of a given pair of (partial) density fields,

$\rho_\alpha(\vec k, t) = \sum_{n=1}^{N_\alpha} \exp\boldsymbol(\text{i} \vec k \cdot \vec r_n(t)\boldsymbol) \/,$

and the total number of particles $N$ . The result is averaged over wavevectors of similar magnitude according to the shells defined by halmd.observables.utility.wavevector.

For details see, e.g., Hansen & McDonald: Theory of simple liquids, chapter 7.4.

class halmd.observables.dynamics.intermediate_scattering_function(args)¶

Construct instance of halmd.observables.dynamics.intermediate_scattering_function.

Parameters:	args (table) – keyword arguments args.density_mode (table) – instance(s) of `halmd.observables.density_mode` args.norm (number) – normalisation factor args.label (string) – module label (optional)
Returns:	instance of intermediate scattering function module

The argument density_mode is an instance or a table of up to 2 instances of halmd.observables.density_mode yielding the partial density modes $\rho_\alpha(\vec k, t)$ and $\rho_\beta(\vec k, t)$ . They must have been constructed with the same instance of halmd.observables.utility.wavevector. Passing only one instance implies $\alpha = \beta$ .

The optional argument label defaults to density_mode[1].label .. "/" .. density_mode[2].label.

disconnect()¶: Disconnect module from profiler.

acquire()¶

Acquire density mode sample.

Returns:	density mode sample

label¶: The module label passed upon construction or derived from the density modes.

desc¶: Module description.

class writer(args)¶

Construct file writer and output wavenumbers.

Parameters:	args (table) – keyword arguments args.file – instance of file writer args.location (string table) – location within file (optional)
Returns:	file writer as returned by `file:writer()`.

The argument location specifies a path in a structured file format like H5MD given as a table of strings. It defaults to {"dynamics", self.label, "intermediate_scattering_function"}.

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Intermediate scattering function¶

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