The structural and electronic properties of $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_3$ under hydrostatic pressure are investigated by means of ab initio $\mathrm{LDA}+\mathrm{U}$ calculations, based on ultrasoft pseudopotentials. Previous theoretical studies have indicated that the local-density approximation (LDA) incorrectly predicts the ambient-pressure $Pnma$ structure of $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_3$ to be metallic and significantly underestimates its Jahn-Teller distortion, when full structural optimization is performed. We find that the $\mathrm{LDA}+\mathrm{U}$ approach corrects such features and provides a good general description of the complex structural changes observed in the $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_3$ $Pnma$ phase under pressure. Consistent with experiment, we find that the off-center shift in the La $x$ coordinates, present at low pressure, disappears at about $15\mathrm{GPa}$. Our results indicate that this reduces the stability of the type-$d$ Jahn-Teller distortion, giving rise to type-$a$ and type-$d$ Jahn-Teller distorted structures which are essentially degenerate in energy above $\sim 15\mathrm{GPa}$. We suggest that this may be a key element in driving the structural transition of the $Pnma$ phase that is observed experimentally at $\sim 15\mathrm{GPa}$.

• Received 27 June 2004

DOI:https://doi.org/10.1103/PhysRevB.71.035101