Aluminum under high pressure. I. Equation of state

A curve of applied pressure $P$ versus lattice constant $a$ is calculated for single-crystal aluminum. It results from an application of the method of structural expansions for deriving the energies of simple metals, a method known to give reasonable results for the elastic constants even at second order in the effective electron-ion interaction. The latter (in the present calculation) is taken from Fermi-surface analysis and it is verified (with this essentially experimental information) that the extant face-centered cubic structure remains the preferred crystalline phase up to the highest pressures considered. Arguments are given to suggest that the $P$ versus $a$ curve should have reasonable a priori accuracy, and can admit of possible improvement if experimental data in the intermediate-pressure region can be provided to refine the (in principle) energy-dependent pseudopotential. At three megabars the lattice constant is reduced by only 22%; the ion cores at this pressure are still very well separated.