Structural and electronic properties of LaMnO3 under pressure: An ab initio LDA+U study

The structural and electronic properties of LaMnO3 under hydrostatic pressure are investigated by means of ab initio LDA+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 LaMnO3 to be metallic and significantly underestimates its Jahn-Teller distortion, when full structural optimization is performed. We find that the LDA+U approach corrects such features and provides a good general description of the complex structural changes observed in the LaMnO3 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 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 similar to15 GPa. We suggest that this may be a key element in driving the structural transition of the Pnma phase that is observed experimentally at similar to15 GPa.