Isotherms of isoelectronic materials, melting, and shear moduli in the megabar pressure range

It is shown that the isotherms of isoelectronic materials in the statistical model converge in the megabar pressure range. The convergence of isotherms is universal and depends neither on the crystallographic structure nor on the specific type of the intermolecular potential. It is pointed out that the majority of compounds and minerals which constitute the Earth's mantle are isoelectronic with neon. The melting curves of isoelectronic materials are parallel to each other. The mutual arrangement of the melting curves depends on the number of atoms in the molecule. Computations of the shear moduli of materials at 1 Mbar show that the materials with small number of electrons per atom have the lowest shear modulus. These materials are preferable for using as pressure-transmitting media in the megabar pressure range.