Step 6 - Set up Refinement

Time to refine. We’ll need two processing layers - one to calculate the g(r) and S(Q) from the simulation, and one to refine it against experimental data.

As noted in the introduction we have neutron-weighted experimental data, so we need a layer to calculate g(r) and neutron-weighted S(Q) for our three experimental datasets:

Layer ⇨ Create ⇨ Correlations ⇨ RDF and Neutron S(Q)

Open the module palette for the layer by clicking the Show Avaliable Modules button at the bottom left of the tab

Drag two additional NeutronSQ modules from the Correlation Functions category to the module list, placing them after the existing NeutronSQ module

We need to set the instrumental broadening in the SQ module first:

Click on the SQ module to select it

Set the QBroadening to OmegaDependentGaussian with a FWHM of 0.02

Now let’s set up the three NeutronSQ modules to calculate what we want:

C₆H₆

Click on the first NeutronSQ module to select it

Double-click on its name and change it to C6H6

In the Reference Data settings group find the Reference keyword, select the file C6H6.mint01 and set the format of the data to mint

C₆D₆

Click on the second NeutronSQ module to select it

Change its name to C6D6

In the Control section click the button for the Isotopologue option

Press the Species button to add the natural isotopologue for the first species present

Change the isotopologue from Natural to C6D6

Find the Reference Data settings group, and for the Reference keyword select the file C6D6.mint01 and set the format of the data to mint

50:50 Mix

Click on the third NeutronSQ module to display its options

Change its name to 5050

In the Control section click the button for the Isotopologue option

Press the Species button to add the natural isotopologue for the first species present

Select either row in the table and click the Isotopologue button to insert the next unused isotopologue (i.e. the deuterated analogue)

The isotopologue mixture you’ve just defined has equal parts (weight = 1.0) of the Natural and C6D6 benzene isotopologues. You can use whatever ratios make sense - Dissolve will always normalise the total weight back to 1.0 internally.

Finally, find the Reference Data settings group and for the Reference keyword select the file 5050.mint01 and set the format of the data to mint

All that remains is to add our EPSR refinement layer:

Layer ⇨ Create ⇨ Refinement ⇨ Standard EPSR

All of the default values set there will be sufficient.

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