Optoelectronics and defect levels in hydroxyapatite by first-principles.

Area of Science:

• Materials Science
• Computational Physics
• Solid State Chemistry

Background:

• Hydroxyapatite (HAp) is vital for bone and teeth, with broad use in prosthetics.
• Accurate understanding of HAp's electronic band structure is needed for advanced applications like photocatalysis.
• Current knowledge of HAp's optoelectronic properties and defect levels is limited.

Purpose of the Study:

• To accurately calculate the electronic band structure and optoelectronic properties of hydroxyapatite.
• To investigate the origin of the conduction band bottom in HAp.
• To determine the impact of exchange-correlation functional choice on defect level calculations.

Main Methods:

• State-of-the-art methodologies including density hybrid-functional theory.
• Many-body perturbation theory within the dynamically screened single-particle Green's function approximation.
• Calculation of defect levels using OH-vacancy as a model.

Main Results:

• Hybrid-DFT functionals significantly improve HAp's band structure, dielectric, and optical properties.
• The conduction band bottom originates from anti-bonding σ* states along ⋯OH-OH-⋯ chains, suggesting a 1D-ice phase.
• Hybrid-DFT and semi-local DFT yield defect transition energy differences of ~2 eV for OH-vacancy.

Conclusions:

• High-quality electron-electron interaction descriptions are essential for accurate electronic and optical property calculations in HAp.
• The findings provide fundamental insights into HAp's electronic behavior, enabling new technological applications.
• The study highlights the critical role of computational methods in advancing materials science.