XRaySQ (Module)

Calculate x-ray-weighted S(Q) and G(r)

Overview

XRaySQ is responsible for taking a set of previously calculated $S (Q)$ from an SQ module and generating a new set of x-ray-weighted structure factors. The total x-ray-weighted structure factor, $F^{X} (Q)$ , is generated through summation of the individual partial x-ray-weighted $S (Q)$ . X-ray-weighted partial and total radial distribution functions are also calculated.

The XRaySQ module does not target any configurations itself - the underlying GR module, referenced by the SQ module, dictates the source configuration data.

Description

Basic Theory

The XRaySQ module calculates the Faber-Ziman partial structure factors weighted by the atomic x-ray scattering lengths, such that

$S_{i j}^{X} (Q) = b_{i} (Q) b_{j} (Q) S_{i j} (Q)$

where $b_{i} (Q)$ and $b_{j} (Q)$ are the Q-dependent form factors of the atom types $i$ and $j$ respectively. In a similar manner, the total x-ray-weighted structure factor is

$F^{X} (Q) = \sum_{i, j, i \geq j}^{N} [2 - δ_{i j}] b_{i} (Q) b_{j} (Q) c_{i} c_{j} S_{i j} (Q)$

Depending on the need, $F^{X} (Q)$ may be normalised to an appropriate constant with the Normalisation keyword.

Instrumental Broadening

The application of instrumental broadening is the responsibility of the source SQ module - see its QBroadening keyword.

Options

Targets

Keyword	Arguments	Default	Description
`SourceSQs`	`Module`	–	Required Source SQ module from which to take unweighted $S (Q)$ .

Form Factors & Normalisation

Keyword	Arguments	Default	Description
`FormFactors`	`XRayFormFactors`	`WK1995`	Atomic form factors to use for weighting
`NormaliseTo`	`NormalisationType`	`None`	Normalisation to apply to the total weighted F(Q). The same normalisation is also applied to supplied reference data following removal (if appropriate) of its own normalisation (see the `ReferenceNormalisedTo` keyword)

Reference Data

Keyword	Arguments	Default	Description
`Reference`	`Data1DFileAndFormat`	–	Format and filename of reference $F (Q)$ data, to be displayed in the GUI alongside calculated data, and made available for other modules to utilise (e.g. `EPSR`
`ReferenceFTDeltaR`	`double`	0.05	Spacing in $r$ to use when generating the Fourier-transform of the $F (Q)$
`ReferenceFTQMax`	`double`	–	Maximum Q value to use when Fourier-transforming the reference $F (Q)$ to its $G (r)$
`ReferenceFTQMin`	`double`	–	Minimum Q value to use when Fourier-transforming the reference $F (Q)$ to its $G (r)$
`ReferenceNormalisedTo`	`NormalisationType`	`None`	Normalisation which has been applied to the reference data
`ReferenceWindowFunction`	`WindowFunction`	`Lorch0`	Window function to apply when Fourier-transforming reference $F (Q)$ to a reference $g (r)$

Export

Keyword	Arguments	Default	Description
`SaveFormFactors`	`bool`	`false`	Save Q-dependent form factors for each atom type pair
`SaveGR`	`bool`	`false`	Save weighted g(r) and G(r). Separate files are written for each partial between atom types $i$ and $j$ , as well as the total.
`SaveReference`	`bool`	`false`	Save the reference data and its Fourier transform
`SaveRepresentativeGR`	`bool`	`false`	Save the representative $G (r)$ obtained from Fourier transform of the calculated $F (Q)$
`SaveSQ`	`bool`	`false`	Save weighted partial and total structure factors. Separate files are written for each partial between atom types $i$ and $j$ , as well as the total.

Last modified July 11, 2023: 1495 Update Docs 1.3 (#1517) (85355211f)