Optical properties of BaTiO₃ at room temperature: DFT modelling

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• Barium titanate (BaTiO3) is a crucial ferroelectric material with significant optical properties.
• Understanding its optical behavior is essential for advanced applications.
• Previous studies often simplified atomic interactions, neglecting dynamic effects.

Purpose of the Study:

• To investigate the impact of atomic motion on the optical properties of tetragonal barium titanate (BaTiO3).
• To calculate and compare optical absorption spectra for static and dynamic lattice conditions.
• To elucidate the mechanisms behind changes in optical absorption due to thermal effects.

Main Methods:

• Utilized density functional theory (DFT) with generalized gradient approximation + on-site Hubbard correlation (GGA + U) and hybrid functionals for static lattice calculations.
• Performed ab initio molecular dynamics (AIMD) simulations using GGA + U to incorporate atomic thermal motion.
• Calculated optical absorption spectra for both static and dynamic BaTiO3 lattice configurations.

Main Results:

• Atomic motion significantly reduces the calculated optical absorption threshold energy.
• Thermal vibrations enable previously "dark" electronic transitions, making them observable.
• Fluctuations in electronic transition energies due to atomic movement further decrease the absorption threshold.

Conclusions:

• Dynamic atomic motion is critical for accurately predicting the optical absorption spectra of BaTiO3.
• The study provides insights into the interplay between lattice dynamics and electronic transitions.
• Observed phenomena may explain features in experimental photoluminescence spectra, particularly related to electron energy dispersion.