Antisite Defects Formation in LaMO₃ (M=Mn, Fe, Ni, and Co) predicted by Fixed-node Diffusion Monte Carlo Method

The properties of transition-metal perovskite crystals are significantly affected by point defects. Therefore, their introduction could potentially tune perovskite crystals for various applications. The most studied defects are the oxygen vacancy and substitutional impurity defects in the La and transition metal sites. In this work, we show theoretically that a transition metal atom at the La site can be formed under certain growth conditions. Using density functional theory (DFT) and fixed-node diffusion Monte Carlo (DMC) methods, we report results for LaMO₃ (M=Mn, Fe, Ni, and Co). In addition, we study magnetism in non-defective perovskite crystals. We establish that only DMC reproduces the experimentally found antiferromagnetic ground state in LaFeO₃, but DFT with PBE and SCAN functionals both predict ferromagnetic ground state.