Occupation matrix control of d- and f-electron localisations using DFT + U

Area of Science:

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

Background:

• Standard density functional theory (DFT) often struggles to accurately describe localized d and f states.
• The DFT + onsite correction (DFT + U) method improves these descriptions but can lead to issues with electronic metastability.
• Metastability arises from multiple possible electron orbital occupations and locations within a material.

Purpose of the Study:

• To develop and validate an occupation matrix control methodology for plane-wave DFT + U calculations.
• To enable precise control over both the site and orbital localization of electrons, particularly for d and f states.
• To address the challenge of electronic metastability in localized electron systems.

Main Methods:

• Utilized a plane-wave density functional theory + onsite correction (DFT + U) approach.
• Implemented an occupation matrix control methodology to dictate electron localization.
• Tested the method on molecular systems (Ti(iii) and Ce(iii) carbonyl clusters) and periodic systems (anatase-TiO2 and CeO2).
• Simulated electron addition and oxygen vacancy formation in periodic systems to study localization effects.

Main Results:

• Successfully simulated and controlled orbital occupation in Ti(iii) and Ce(iii) carbonyl clusters.
• Demonstrated accurate control of both orbital and site localization in periodic TiO2 and CeO2 systems.
• Investigated electronic metastability and orbital degeneracies under various conditions, including defect formation.
• Validated the effectiveness of the occupation matrix control in managing electron localization.

Conclusions:

• The occupation matrix control methodology provides a robust way to simulate localized d and f states within DFT + U.
• This approach effectively manages electronic metastability and allows for precise control over electron localization in complex materials.
• The method is crucial for accurate electronic structure calculations involving localized electrons and defects.