A RMC study of glassy ZnCl_{2} has already been published.
The same neutron data was used, as in this previous work.
Because in this early
study, the model was small (324 atoms),
a much larger one was
built here with 1950 atoms
in a cubic box with L
= 39.906 Å.
Strategy
Strategy is quite important when using RMC, and the normal way for imposing a 4connected threedimensional network is :
Another approach was deliberately used here, in order to verify if a good fit would be obtained also when edge sharing could occur between [ZnCl_{4}] tetrahedra.
Obtaining that all the Zn atoms form [ZnCl_{4}] tetrahedra was quite long (several days on a PentiumII 333MHz).
Then, the RMCA program
was run against the neutron diffraction data, obtaining finally an excellent
agreement with Rp = 0.76 %.
Looking accurately to this model reveals that the systematic sharing of exactly two Zn atoms by Cl atom is far from being realized :
Repartition of neighbouring [ZnCl_{4}] tetrahedra in the final "classic" RMC model for ZnCl_{2}, starting from a pseudo random configuration.






















NT is the number of tetrahedra sharing N chlorine atoms with other tetrahedra. A perfect 4connected 3D net would have corresponded to NT = 650 for N = 4.
One tetrahedron among 650 is isolated and clusters were built of which the biggest are 5 tetrahedra sharing each of their Cl atoms with 2 other tetrahedra (8 neighbours). One tetrahedron has even 9 other tetrahedra as next neighbours :

A total of 37 tetrahedra share one edge and 2 tetrahedra share 2 edges. So that, the building conditions were unable to ensure the corner sharing exclusivity, if we expected it.
Nevertheless, the fit is almost perfect.
On the other hand, the ZnCl_{2} RDM model (Rp = 2.40 %), built up from the dZnCl_{2} structure, corresponds to a perfect 4connected threedimensional network.
Result from the ARITVE
program :
That RDM model was expanded
to 1728 atoms,
before to realize the
RMC approach,
obtaining finally the
expected low reliability value Rp = 1.09 %.
Projection of the RMC model for glassy ZnCl_{2}, starting from the d ZnCl_{2} RDM model.
The distorted triangular tunnels are finger print of the RDM starting model.