Linear and second-order nonlinear optical properties of ionic organic crystals

Area of Science:

• Materials Science
• Computational Chemistry
• Nonlinear Optics

Background:

• Ionic organic crystals like DAST, DSTMS, and DAPSH are crucial for nonlinear optical applications.
• Understanding their optical properties requires accurate theoretical models that account for crystal structure and electronic interactions.

Purpose of the Study:

• To calculate the linear and second-order nonlinear optical susceptibilities (χ((1)) and χ((2))) of DAST, DSTMS, and DAPSH.
• To develop and validate a multi-scale computational approach for predicting these properties.
• To elucidate the influence of counterions and crystal environment on optical responses.

Main Methods:

• A two-step multi-scale procedure combining ab initio/DFT for ion properties and classical electrostatics for crystal environment effects.
• Second-order Møller-Plesset perturbation theory for ionic properties.
• Point charge models to simulate dressing field effects.

Main Results:

• Excellent agreement between calculated and experimental optical susceptibilities when using the validated multi-scale method.
• The study explains the superior χ((2)) response of DAPSH compared to DAST and DSTMS.
• Inclusion of dressing fields decreases χ((2)) in ionic crystals but increases it in molecular crystals.
• The counterion's nature and position significantly impact linear and nonlinear optical susceptibilities.

Conclusions:

• The developed multi-scale approach accurately predicts optical properties of ionic organic crystals.
• This method provides insights into structure-property relationships, particularly the role of counterions.
• The findings guide the design of novel materials for advanced nonlinear optical applications.