Electronic and Vibrational Nonlinear Optical Properties of Five Representative Electrides

Area of Science:

• Materials Science
• Quantum Chemistry
• Nonlinear Optics

Background:

• Electrides possess unique electronic structures with delocalized excess electrons.
• These structures are known to exhibit substantial electronic nonlinear optical (NLO) properties.
• A comprehensive understanding of their vibrational NLO properties is crucial.

Purpose of the Study:

• To determine and analyze the vibrational NLO properties of representative electrides.
• To compare vibrational NLO properties with electronic NLO properties.
• To investigate factors influencing these properties, such as anharmonicity and charge distribution.

Main Methods:

• Computational analysis of static and dynamic vibrational (hyper)polarizabilities.
• Utilized the nuclear relaxation method with field-induced coordinates and infinite optical frequency approximation.
• Employed UB3LYP level of theory with a hybrid Pople basis set for calculations.

Main Results:

• Static vibrational hyperpolarizabilities (βvec and γ∥) generally exceed static electronic counterparts by up to an order of magnitude.
• Dynamic vibrational hyperpolarizabilities show a smaller, yet significant, ratio compared to electronic values.
• Ratios are near unity for intensity-dependent refractive index (IDRI) and dc-Kerr effects, and lower but important for dc-Pockels and electric field induced second harmonic (EFISH) effects.

Conclusions:

• Vibrational NLO properties are a significant contributor to the overall NLO response in electrides.
• The study highlights the importance of considering vibrational contributions alongside electronic ones for accurate NLO characterization.
• Anharmonicity and alkali atom dynamics play a role in modulating these NLO properties.