Ab initio dynamics study of poly-para-phenylene vinylene

Area of Science:

• Computational Materials Science
• Condensed Matter Physics
• Polymer Science

Background:

• Poly-para-phenylene vinylene (PPV) is a conjugated polymer with significant optoelectronic applications.
• Understanding its vibrational and electronic properties is crucial for device performance.
• Previous studies lacked detailed assignments for all observed vibrational modes in crystalline PPV.

Purpose of the Study:

• To investigate the ab initio dynamics of poly-para-phenylene vinylene (PPV) in both isolated chain and crystalline states.
• To assign hitherto unidentified vibrational modes observed in experimental studies of crystalline PPV.
• To calculate and analyze the polarizability, permittivity tensors, and effective charges of PPV.

Main Methods:

• Density-functional perturbation theory (DFPT) framework for ab initio dynamics.
• Calculation of vibrational modes, polarizability, and permittivity tensors.
• Comparison of dynamical Born effective charges with Mulliken population analysis charges.

Main Results:

• Calculated vibrational modes for isolated PPV chains largely match experimental modes of crystalline PPV.
• Successfully assigned previously unidentified experimental vibrational modes using calculations on crystalline PPV.
• Computed polarizability and permittivity tensors agree with typical values for conjugated polymers; effective charges are deemed more suitable for dynamical studies.

Conclusions:

• Crystalline packing effects significantly influence the lattice dynamics of PPV, leading to notable differences in infrared-absorption spectra compared to isolated chains.
• Dynamical Born effective charges provide a more appropriate description for studying PPV system dynamics than Mulliken charges.
• The study provides a comprehensive understanding of PPV's vibrational and electronic properties, aiding future material design and application.