Reaction pathways in the solid state and the Hubbard U correction

Area of Science:

• Materials Science
• Computational Materials Science
• Solid-State Physics

Background:

• Density Functional Theory (DFT) is crucial for predicting material properties.
• Generalized Gradient Approximation (GGA) is a common DFT functional.
• The Hubbard U correction is often applied to improve GGA accuracy for correlated materials.

Purpose of the Study:

• To investigate the influence of the Hubbard U correction on vacancy defect migration barriers.
• To understand how d-orbital occupation affects migration barrier energies.
• To identify limitations of GGA DFT with Hubbard U corrections for modeling reactive pathways.

Main Methods:

• Utilizing generalized gradient approximation density functional theory (GGA DFT).
• Applying the Hubbard U correction to transition metal oxide semiconductors.
• Analyzing vacancy defect migration barriers in SrTiO3 and ZnO.

Main Results:

• Hubbard U correction introduces instabilities in migration barriers, dependent on d-orbital occupation.
• A sudden increase in migration barrier energy for SrTiO3 above a U threshold was observed.
• Similar, but less pronounced, effects were found in ZnO, requiring larger U values.

Conclusions:

• The Hubbard U correction's impact on migration barriers is sensitive to transition metal d-orbital occupation.
• GGA DFT with Hubbard U corrections has limitations for modeling reactive pathways in oxides.
• Careful consideration of U values is necessary for accurate defect migration studies.