Stacked clusters of polycyclic aromatic hydrocarbon molecules

Area of Science:

• Computational chemistry
• Astrochemistry
• Materials science

Background:

• Polycyclic aromatic hydrocarbons (PAHs) are abundant in space.
• Understanding PAH cluster formation is crucial for astrophysics and materials science.
• Accurate modeling requires considering intermolecular forces and electrostatic interactions.

Purpose of the Study:

• To model polycyclic aromatic hydrocarbon (PAH) clusters using computational methods.
• To investigate the structural stability and aggregation behavior of PAH clusters.
• To explore the influence of electrostatic interactions on PAH cluster formation.

Main Methods:

• Explicit all-atom potentials with rigid-body approximation for PAH molecules (pyrene to circumcoronene).
• Incorporation of repulsion-dispersion and electrostatic interactions from density functional theory (DFT) calculations.
• Global optimization using basin-hopping and parallel tempering Monte Carlo methods.

Main Results:

• PAH molecules predominantly form stable stacked motifs.
• A structural transition from 1D stacks to 3D shapes occurs at larger cluster sizes.
• Larger aggregates exhibit packing similar to bulk benzene; anisotropy presents optimization challenges.

Conclusions:

• Stacking is the primary stable configuration for PAH clusters.
• Cluster structure evolves with size, transitioning to 3D arrangements.
• Findings inform astrophysical models and the design of novel materials.