  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. This not only explains the ground
state of SrRuO3 but also contributes to rationalize why most ABO3 perovskites
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.
