Many competing ceria (110) oxygen vacancy structures: from small to large supercells

Area of Science:

• Materials Science
• Surface Science
• Computational Chemistry

Background:

• Cerium dioxide (CeO2) is a crucial material in catalysis and solid oxide fuel cells.
• Oxygen vacancies in CeO2 significantly influence its electronic and ionic properties.
• Understanding vacancy formation and behavior is key to optimizing CeO2-based technologies.

Purpose of the Study:

• Investigate the structural and electronic properties of single oxygen vacancies on the CeO2(110) surface.
• Determine the preferred local minimum structures for vacancies and associated Ce(III) ions.
• Assess the impact of supercell size on calculated vacancy properties.

Main Methods:

• Periodic Density Functional Theory with the Hubbard U (DFT+U) method was employed.
• Studies were conducted using multiple supercell sizes (p(2×1) to p(3×3)).
• A two-stage optimization procedure was used to achieve electron trapping.

Main Results:

• Three distinct geometrical structures for oxygen vacancies were identified.
• Various Ce(III) ion localization patterns were observed, with some being novel.
• An unsymmetric bridge structure with specific Ce(III) neighbors emerged as the ground state in most supercells.
• Formation energies varied significantly with supercell size (up to ~1 eV).

Conclusions:

• The choice of supercell size critically affects the calculated vacancy structures and energies.
• The ground state structure is sensitive to supercell dimensions, indicating finite-size effects.
• Accurate modeling requires careful consideration of supercell size and potential errors.