Structural stability and defect energetics of ZnO from diffusion quantum Monte Carlo

Area of Science:

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

Background:

• Density Functional Theory (DFT) approximations often struggle with accurately describing material properties and defect energetics in ZnO.
• Accurate theoretical characterization of defects like oxygen vacancies and interstitials is crucial for understanding and engineering ZnO-based materials.

Purpose of the Study:

• To apply the many-body ab initio diffusion quantum Monte Carlo (DMC) method to study Zn and ZnO crystals under pressure.
• To investigate the energetics of oxygen vacancy, zinc interstitial, and hydrogen impurities in ZnO.
• To assess the accuracy and practicality of DMC compared to DFT for material properties and defect characterization.

Main Methods:

• Many-body ab initio diffusion quantum Monte Carlo (DMC) calculations.
• Study of Zn and ZnO crystals under pressure.
• Energetics calculations for oxygen vacancy, zinc interstitial, and hydrogen impurities in ZnO.

Main Results:

• DMC shows excellent agreement with experimental measurements (within 0.3 eV) for various properties, including the ZnO band-gap and ionization potentials.
• DMC predicts the oxygen vacancy as a deep donor with a formation energy of 5.0(2) eV under O-rich conditions.
• DMC indicates low concentrations for zinc interstitial and hydrogen impurities under specific conditions due to high formation energies (>1.4 eV).

Conclusions:

• DMC is an accurate and practical method for characterizing material properties and defects in ZnO, surpassing limitations of standard DFT approximations.
• While hybrid DFT functionals can provide qualitative descriptions, quantitative differences in defect formation energies compared to DMC can exceed 0.5 eV.
• The study validates DMC as a reliable tool for predicting defect behavior and material properties in ZnO.