Self-trapped excitons in diamond: A Δ-SCF approach

Area of Science:

• Computational materials science
• Solid-state physics
• Quantum chemistry

Background:

• Understanding excited states in diamond is crucial for optoelectronic applications.
• Previous theoretical studies have limitations in accurately predicting excited state properties.

Purpose of the Study:

• To perform the first variationally based predictions of diamond's lowest excited state.
• To investigate both unrelaxed (optical) and structurally relaxed (thermal) configurations.
• To analyze charge and spin distributions, bandgaps, and luminescence properties.

Main Methods:

• Direct delta-self-consistent-field (SCF) calculations.
• Utilized B3LYP, PBE0, HSE06, and GGA functionals.
• Mulliken population analysis for charge and spin distribution.

Main Results:

• The B3LYP functional accurately predicted the optical excited state energy (7.27 eV) and insulating behavior with bandgaps of 5.6-5.8 eV.
• Excited states exhibit strong excitonic character with significant charge redistribution.
• Calculated Stokes shift (0.47 eV) and Γ-point luminescence energy (6.89 eV) align with experimental values.
• Predicted bi- and triexcitons are bound states, potentially leading to exciton condensation.

Conclusions:

• The study provides accurate theoretical predictions for diamond's excited states and luminescence.
• Findings support the excitonic nature of excited states and offer insights into exciton condensation.
• The employed theoretical framework is robust for studying excited-state properties in semiconductors.