Polymer Optical Constants from Long-Range Corrected DFT Calculations.

Area of Science:

• Materials Science
• Computational Chemistry
• Polymer Physics

Background:

• Accurate refractive index prediction is crucial for polymer characterization and optical applications.
• Existing methods often struggle with the complexity of polymer structures and electronic properties.

Purpose of the Study:

• To develop a robust computational methodology for calculating the refractive indices of polymers.
• To assess the accuracy of long-range corrected functionals in predicting polymer polarizability.
• To investigate the impact of end-group corrections on model accuracy.

Main Methods:

• Utilizing the Lorentz-Lorenz equation for refractive index calculations.
• Employing long-range corrected functionals to predict polarizability of polymer repeat units.
• Implementing end-effect corrections in polymer models.
• Comparing different exchange-correlation functionals (e.g., 100% Hartree-Fock, CAM-B3LYP).

Main Results:

• The proposed methodology achieves accuracy comparable to molecular liquids (approx. 1% mean absolute deviation).
• Functionals with 100% Hartree-Fock exchange are optimal for aromatic/hydrogen-deficient polymers.
• CAM-B3LYP performs well for hydrogen-rich polymers.
• Excellent agreement was found for polystyrene, poly(methyl methacrylate), and CYTOP, with low root-mean-square deviations.

Conclusions:

• The developed methodology provides a reliable approach for predicting polymer refractive indices.
• The choice of computational functional significantly impacts prediction accuracy based on polymer composition.
• End-effect corrections are vital for accurate modeling of polymer repeat units.