  By using first-principles methods based on density functional theory we
revisited the zero-temperature phase diagram of stoichiometric SrCoO3, a
ferromagnetic metallic perovskite that undergoes significant structural,
electronic, and magnetic changes as its content of oxygen is decreased. We
considered both bulk and epitaxial thin film geometries. In the bulk case, we
found that a tetragonal P4/mbm phase with moderate Jahn-Teller distortions and
c/a ratio of ~1/sqrt{2} is consistently predicted to have a lower energy than
the thus far assumed ground-state cubic Pm-3m phase. In thin films, we found
two phase transitions occurring at compressive and tensile epitaxial strains.
However, in contrast to previous theoretical predictions, our results show
that: (i) the phase transition induced by tensile strain is isostructural and
involves only a change in magnetic spin order (that is, not a metallic to
insulator transformation), and (ii) the phase transition induced by compressive
strain comprises simultaneous structural, electronic and magnetic spin order
changes, but the required epitaxial stress is so large (<-6%) that is unlikely
to be observed in practice. Our findings call for a revision of the
crystallographic analysis performed in fully oxidised SrCoO3 samples at low
temperatures, as well as of previous first-principles studies.
