Static structure factor¶

The module computes the static structure factor

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

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

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

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 4.1.

class halmd.observables.ssf(args)¶

Construct instance of halmd.observables.ssf.

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

The argument density_mode is an instance or a table of 1 or 2 instances of halmd.observables.density_mode yielding the partial density modes $\rho_\alpha(\vec k)$ and $\rho_\beta(\vec k)$ . 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 static structure factor module from profiler.

sampler¶: Callable that yields the static structure factor from the current density modes.

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

class writer(args)¶

Write time series of static structure factor to file.

Parameters:	args (table) – keyword arguments args.file – instance of file writer args.location (string table) – location within file (optional) args.every (number) – sampling interval
Returns:	instance of density mode writer

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

disconnect()¶: Disconnect static structure factor writer from observables sampler.

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Static structure factor¶

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