Existence of La-site antisite defects in $$\hbox{LaMO}_3$$ ($$\hbox{M} = \hbox{Mn}$$, Fe, and Co) predicted with many-body diffusion quantum Monte Carlo

The properties of $$\hbox{LaMO}_3$$ LaMO 3 (M: 3 d transition metal) perovskite crystals are significantly dependent on point defects, whether introduced accidentally or intentionally. The most studied defects in La-based perovskites are the oxygen vacancies and doping impurities on the La and M sites. Here, we identify that intrinsic antisite defects, the replacement of La by the transition metal, M, can be formed under M-rich and O-poor growth conditions, based on results of an accurate many-body ab initio approach. Our fixed-node diffusion Monte Carlo (FNDMC) calculations of $$\hbox{LaMO}_3$$ LaMO 3 ( $$\hbox{M} = \hbox{Mn}$$ M = Mn , Fe, and Co) find that such antisite defects can have low formation energies and are magnetized. Complementary density functional theory (DFT)-based calculations show that Mn antisite defects in $$\hbox{LaMnO}_3$$ LaMnO 3 may cause the p -type electronic conductivity. These features could affect spintronics, redox catalysis, and other broad applications. Our bulk validation studies establish that FNDMC reproduces the antiferromagnetic state of $$\hbox{LaMnO}_3$$ LaMnO 3 , whereas DFT with PBE (Perdew–Burke–Ernzerhof), SCAN (strongly constrained and appropriately normed), and the LDA+ U (local density approximation with Coulomb U ) functionals all favor ferromagnetic states, at variance with experiment.