First-principles study of the lattice dynamical properties of strontium ruthenate

By means of first-principles calculations, various properties of SrRuO3 are investigated,
focusing on its lattice dynamical properties. Despite having a Goldschmidt tolerance factor
very close to 1, the phonon dispersion curves of the high-temperature cubic phase of SrRuO3
show strong antiferrodistortive instabilities. The energetics of metastable phases with different
tilt patterns are discussed, concluding that the coupling of oxygen rotation modes with
anti-polar Sr motion plays a key role in stabilizing the Pnma phase with respect to alternative
rotation patterns. Our systematic analysis confirms previous expectations and contributes to
rationalizing better why many ABO3 perovskites, including metallic compounds, exhibit an
orthorhombic ground state. The zone-center phonon modes of the Pnma phase have been
computed, from which we propose partial reassignment of available experimental data. The
full dispersion curves have also been obtained, constituting benchmark results for the
interpretation of future measurements and providing access to thermodynamical properties.