Pressure strongly modifies electronic and optical properties of solids. In this work we report ab initio time-dependent density-functional theory calculations of the dielectric response of the high-pressure metallic phase of aluminum hydride $\left({\text{AlH}}_3\right)$ within the random-phase approximation. Besides the conventional free-electronlike plasmon, which is highly damped, low-energy transitions between states near the Fermi level that appear in this metallized phase give rise to a low-energy undamped collective mode. This feature is expected to induce an abrupt edge in the experimentally measured reflectivity just below 1 eV and also affect electronic correlations close to the Fermi energy. Our work shows that ${\text{AlH}}_3$ is basically a hydrogen sublattice weakly perturbed by Al atoms.

• Received 28 June 2010

DOI:https://doi.org/10.1103/PhysRevB.82.085113