Ab initio calculations of elastic constants and thermodynamic properties of bcc, fcc, and hcp Al crystals under pressure

We have performed ab initio electronic structure and total-energy calculations for bcc, fcc, and hcp Al structures to study the equations of state, volume dependences of elastic constants, and relative stability diagram for these structures. A technique for elastic constant calculation in the case of initial isotropic pressure is presented. In this study we used the accurate full-potential linear muffin-tin orbital method to describe electrons of the crystal and the Debye treatment of the vibrating lattice. The volume dependence of the Debye temperature is derived from the volume dependence of the elastic constants. Our calculations show that at pressures of 1-2 Mbar and temperatures of about 1000 K and higher, the aluminium structure must have a lower symmetry than the structures considered.