Point defects in CaF2 and CeO2 investigated by the periodic electrostatic embedded cluster method

Area of Science:

• Computational materials science
• Solid-state chemistry
• Quantum chemistry

Background:

• Accurate modeling of point defects in crystalline materials is crucial for understanding their properties.
• Periodic electrostatic embedding methods offer a way to treat localized defects within extended periodic systems.
• Previous methods often face challenges in balancing accuracy, computational cost, and system size.

Purpose of the Study:

• To present and validate a periodic electrostatic embedding scheme using the periodic fast multipole method (PFMM).
• To investigate the convergence of material properties with cluster size for calcium fluoride models.
• To apply the embedded cluster method to calculate oxygen vacancy formation energies and electron localization in cerium dioxide (CeO2).

Main Methods:

• Development and implementation of a periodic electrostatic embedding scheme.
• Utilized the periodic fast multipole method (PFMM) for efficient electrostatics calculations.
• Applied the PBE0 functional within the embedded cluster approach to model CeO2 and its oxygen vacancies.

Main Results:

• Demonstrated convergence of electron density, density of states, electronic excitations, and defect formation energies with increasing cluster size for CaF2.
• Calculated oxygen vacancy formation energies in bulk CeO2 (3.0 eV) and on the (111) surface (3.3 eV).
• Determined the formation energy for subsurface defects (3.33 eV, singlet open shell) and analyzed Ce 4f electron localization near vacancies.

Conclusions:

• The presented periodic electrostatic embedding scheme provides an accurate and efficient approach for defect studies.
• The method successfully models oxygen vacancies in CeO2, with localized Ce 4f states near surface/subsurface vacancies.
• The computational cost remains low, with embedding calculations under 30 seconds on a single CPU for large clusters.