Bulk Aluminum at High Pressure: A First-Principles Study

TL;DR

This study uses first-principles calculations to explore the behavior and phase transitions of aluminum under extremely high pressures up to 2500 GPa, relevant for various scientific fields.

Contribution

It provides detailed predictions of aluminum's equations of state, phase transition pressures, and phonon behavior at high pressures using density-functional theory.

Findings

Predicted phase transition pressures for fcc, bcc, and hcp aluminum.

Identified pressure at which core overlaps become relevant.

Predicted phonon softening indicating a Born instability at 725 GPa.

Abstract

The behavior of metals at high pressure is of great importance to the fields of shock physics, geophysics, astrophysics, and nuclear materials. In order to further understand the properties of metals at high pressures we studied the equation of state of aluminum using first-principles techniques up to 2500 GPa, pressures within reach of the planned L.L.N.L. National Ignition Facility. Our simulations use density-functional theory and density-functional perturbation theory in the generalized gradient approximation at 0K. We found core overlaps to become relevant beyond pressures of 1200 GPa. The equations of state for three phases (fcc, bcc, and hcp) were calculated predicting the fcc-hcp, fcc-bcc, and hcp-bcc transitions to occur at 215 GPa, 307 GPa, and 435 GPa respectively. From the phonon dispersions at increasing pressure, we predict a softening of the lowest transverse acoustic vibrational mode along the [110] direction, which corresponds to a Born instability of the fcc phase at 725 GPa.