Linear and nonlinear optical response of LiNbO3 calculated from first principles

Area of Science:

• Condensed matter physics
• Materials science
• Computational physics

Background:

• Ferroelectric lithium niobate (LiNbO3) is a crucial material for nonlinear optics and photonics.
• Accurate theoretical prediction of its optical properties is essential for material design and application.
• First-principles calculations offer a powerful tool for understanding material behavior at the electronic level.

Purpose of the Study:

• To theoretically calculate the dielectric function and second-harmonic generation (SHG) spectrum of LiNbO3.
• To investigate the role of quasiparticle effects and self-energy corrections in predicting these properties.
• To compare theoretical predictions with experimental measurements for validation.

Main Methods:

• Density functional theory (DFT) for electronic structure calculations.
• The GW approximation to incorporate quasiparticle corrections.
• Solution of the Bethe-Salpeter equation for the dielectric function.
• Calculation of the SHG spectrum within the independent (quasi) particle approximation and with self-energy effects.

Main Results:

• The calculated dielectric function shows excellent agreement with experimental data.
• The SHG spectrum predicts significant nonlinear coefficients above 1.5 eV.
• Inclusion of self-energy effects in the nonlinear response calculation improves agreement with experimental SHG spectra.

Conclusions:

• First-principles calculations, particularly with GW and Bethe-Salpeter equation methods, accurately describe the dielectric properties of LiNbO3.
• Theoretical predictions of SHG are reliable, especially when self-energy effects are considered.
• This work validates computational approaches for predicting nonlinear optical properties of ferroelectric materials.