Simulate / reproduce details of the A. A. van Well Argon dataset

In #621 we are verifying / reproducing during a full Argon refinement.

However as highlighted in that issue by @patrick-austin there may be some smaller but important concerns with s(q,omega) calculation as observed when run argon simulation to reproduce: Table V and left figure in FIG. 13 in A. A. van Well, P. Verkerk, L. A. de Graaf, J.-B. Suck, and J. R. D. Copley. Phys. Rev. A 31, 3391, published May 1985. These data are stored in https://github.com/MDMCproject/MDMCv0.2_pilot/blob/master/tests/test_data/experimental_data/Well_s_q_omega_Ar_data.xml

As can be seen in #621 the calculated S(q,w) has a pronounced peak at small q and differ in that respect from the observed data in FIG 13 in above cited paper:


This might just be an artefact of how the simulation is run (hopefully) rather than a bug, but need to be understood / verified, which can be done in parallel with work on #621.

Also, when simulating argon with MDMC fortran code this small q difference is not observed, see Figure 1 in https://epubs.stfc.ac.uk/manifestation/36113917.