Similarities and contrasts between critical point behavior of heavy fluid alkalis and d-dimensional Ising model

A brief summary is first given of recent progress in establishing the near-critical point behavior of the fluid alkalis Rb and Cs. Departure from the law of Rectilinear Diameters is emphasized, along with its consequences for theories emphasizing homogeneity and scaling. The behavior as the critical points of Rb and Cs are approached is compared and contrasted with the d-dimensional Ising model.     

Low-coordination phases of both crystalline and fluid states of alkali metals under extreme conditions of high and low densities,respectively

After a brief summary of early work, involving the present authors, relating to low coordination phases of some alkalis in either dense crystalline states at high pressure (e.g. Li) or low density metallic fluids near criticality (Cs and Rb), contact is made with the very recent density functional study by Pickard and Needs (Phys. Rev. Lett. 102, 146401 (2009)). Whereas these authors predict three- and four-fold coordination numbers for extremely high pressure crystalline phases of Li, we stress here the remarkable behaviour of the heavy alkali metallic fluids Cs and Rb along the liquid–vapour coexistence curve towards the critical point. Coordination numbers ～8?10 near melting then reduce, as the density is lowered, to 2 at or near the critical point.