First-Principles Modeling of Polaron Formation in TiO₂ Polymorphs

Area of Science:

• Solid-state physics and chemistry
• Computational materials science
• Electronic properties of materials

Background:

• Accurate modeling of electron and hole polarons is crucial for understanding charge transport in semiconductors.
• Existing methods often struggle with computational cost and accuracy for complex material phases.
• Polaron formation significantly impacts material properties relevant to electronic devices.

Purpose of the Study:

• To develop a computationally efficient and predictive methodology for modeling polaron formation and properties.
• To apply this method to various stable and metastable phases of titanium dioxide (TiO2).
• To investigate the localization and trapping energies of electron and hole polarons across different TiO2 structures.

Main Methods:

• Nonempirical and self-consistent optimization of the fraction of Hartree-Fock exchange (α) in hybrid functionals.
• Ensuring the generalized Koopmans' condition and minimizing self-interaction error.
• Application to anatase, rutile, brookite, TiO2(H), TiO2(R), and TiO2(B) phases.

Main Results:

• Predicted electron polaron formation in rutile, TiO2(H), and TiO2(R) with specific trapping energies and localization patterns.
• Predicted hole polaron formation in anatase, brookite, TiO2(H), TiO2(R), and TiO2(B) with varying trapping energies and localization.
• Achieved accurate band gaps for anatase, rutile, and brookite, within 6% of experimental values, using a transferable α = 0.115.

Conclusions:

• The developed methodology provides a computationally accessible route for accurate polaron modeling.
• The findings offer insights into charge trapping mechanisms in diverse TiO2 polymorphs.
• This approach is suitable for studying complex defects in materials relevant to technological applications.