Electronic structure and phonons in FeTi at high pressure

The FeTi system is amenable to computational investigations due to its simple crystal structure and minimalist Fermi surface. A thermally-driven electronic topological transition that results in anomalous phonon softening was recently reported to occur in FeTi at elevated temperatures as new features appear in the Fermi surface and new spanning vectors increase electronic screening of particular phonon modes. We investigated the pressure dependence of the electronic structure and the phonon dispersions using density functional theory and uncovered an octahedral splitting with an energy difference that increases with pressure and a Kohn anomaly with a wavevector that decreases with pressure. The calculated Fe partial phonon density of states are in agreement with nuclear-resonant inelastic x-ray scattering measurements and show that the phonons stiffen at different rates.