Optical Properties of Neutral F Centers in Bulk MgO with Density Matrix Embedding

Area of Science:

• Solid State Physics
• Computational Materials Science
• Quantum Chemistry

Background:

• Neutral oxygen vacancies (F0 centers) are crucial defects in Magnesium Oxide (MgO) crystals.
• Understanding their optical properties is key to MgO's applications in electronics and optics.
• Previous studies often lack high-accuracy theoretical predictions for these defect states.

Purpose of the Study:

• To accurately calculate the optical spectra of F0 centers in bulk MgO.
• To compare theoretical predictions with experimental absorption and emission data.
• To elucidate the electronic transitions and decay pathways involved.

Main Methods:

• Utilizing Density Matrix Embedding Theory (DMET) for defect modeling.
• Solving the impurity Hamiltonian with multireference methods: Complete Active Space Self-Consistent Field (CASSCF) and second-order n-electron valence state perturbation theory (NEVPT2).
• Employing a double extrapolation scheme to determine defect-localized vertical excitation energies at non-embedding and thermodynamic limits.

Main Results:

• The extrapolated NEVPT2-DMET vertical excitation energy of 5.24 eV shows excellent agreement with experimental absorption maxima at 5.03 eV.
• Calculated excitation energy of 2.89 eV for the relaxed triplet defect-localized state is close to the experimental emission at 2.4 eV.
• The small discrepancy suggests the involvement of a triplet-singlet decay pathway in the luminescence process.

Conclusions:

• The theoretical framework accurately reproduces experimental optical spectra for F0 centers in MgO.
• The findings provide strong evidence for a triplet-singlet decay mechanism governing luminescence.
• This work offers a reliable computational approach for studying point defects in oxides.