Computational workflows for novel materials: Case study for lanthanide manganese perovskites

Robust computational workflows are important for explorative computational studies, especially for cases where detailed knowledge of the system structure or other properties is not available. In this work, we propose a computational protocol for appropriate method selection in density functional theory, based strictly on open source software. The protocol is applicable to perovskite systems and does not require a starting crystal structure. We validate this protocol using a set of crystal structures of lanthanide manganates, confirming that PBE+U is a reasonable choice for this purpose, along with the OLYP and HCTH120 density functional approximations. We also highlight that +U values derived from linear response theory are robust and their use leads to improved results. We investigate whether the performance of methods for predicting the bond length of related gas phase diatomics correlates with their performance for bulk structures, showing that care is required when interpreting benchmark results. Finally, using defective LaMnO3 as a case study, we investigate whether the three selected methods can computationally reproduce the experimentally determined fraction of MnIV+ at which the orthorhombic to rhombohedral phase transition occurs. The results are mixed, with HCTH120 providing a good quantitative agreement, while PBE+U better capturing the qualitative aspects of this phase transition.