Diffusion quantum Monte Carlo calculations of SrFeO₃ and LaFeO₃

Area of Science:

• Materials Science
• Computational Physics
• Solid-State Chemistry

Background:

• Oxygen vacancies significantly influence the properties of perovskite oxides like SrFeO3 and LaFeO3.
• Accurate theoretical prediction of these defects is crucial for materials design.

Purpose of the Study:

• To calculate the equations of state, formation energy, and migration energy barrier of oxygen vacancies in SrFeO3 and LaFeO3.
• To compare the accuracy of Diffusion Quantum Monte Carlo (DMC) with various Density Functional Theory (DFT) approximations.

Main Methods:

• Diffusion Quantum Monte Carlo (DMC) calculations.
• Density Functional Theory (DFT) approximations (including semi-local and local density approximations).
• Calculation of cohesive energies, structural properties, formation energies, and migration energy barriers.

Main Results:

• DMC accurately reproduced experimental cohesive energies (<0.23(5) eV error) and structural properties (<1% error).
• DMC formation energies for oxygen vacancies were 1.3(1) eV (SrFeO3) and 6.24(7) eV (LaFeO3).
• DFT approximations underestimated vacancy formation energies by ~1.5 eV and tended to overdelocalize electrons around defects.

Conclusions:

• DMC provides a highly accurate method for studying oxygen vacancies in perovskite oxides.
• DFT approximations introduce significant errors in calculating defect properties, particularly concerning electron localization.
• Steric and electrostatic effects are the primary drivers of oxygen vacancy migration barriers in these materials.