Intramolecular vibrational force fields for linear carbon chains through an adaptative linear scaling scheme

Area of Science:

• Computational Chemistry
• Materials Science
• Solid-State Physics

Background:

• Oligoynes are carbon-based materials with unique electronic and vibrational properties.
• Understanding their vibrational force fields is crucial for predicting their behavior and applications.
• Previous studies have explored oligoyne properties, but detailed vibrational force field analysis is ongoing.

Purpose of the Study:

• To investigate the vibrational force fields of hydrogen-capped oligoynes using computational methods.
• To determine how interaction force constants change with chain length and bond distance.
• To develop accurate predictive models for oligoyne vibrational spectra.

Main Methods:

• Density functional theory (DFT) calculations were employed.
• Vibrational force fields and interaction force constants were computed for oligoynes of varying lengths.
• The influence of exchange-correlation functionals and basis sets was assessed.
• A scaling procedure was developed to improve quantitative agreement.

Main Results:

• Interaction force constants between CC stretching coordinates decrease slowly with increasing distance.
• The study discusses frequency dispersion of longitudinal optical (LO) phonons in infinite polyyne chains.
• Results are related to the spectral behavior of finite-size oligoyne molecules.
• New force fields show excellent quantitative agreement with experimental data.

Conclusions:

• The developed force fields provide a sound assignment for alpha and beta lines in oligoyne spectra.
• The findings offer a deeper understanding of vibrational properties in carbon-rich materials.
• This work establishes a reliable computational approach for predicting oligoyne vibrational spectra.