Structures and Energetics of Neutral and Cationic Pyrene Clusters

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Pyrene clusters are model systems for studying polycyclic aromatic hydrocarbon (PAH) behavior.
• Understanding the structure and stability of neutral and charged molecular clusters is crucial for various chemical and physical processes.

Purpose of the Study:

• To investigate the low-energy structures of neutral and cationic pyrene clusters up to seven molecules.
• To analyze the structural differences between neutral and cationic pyrene clusters.
• To correlate structural features with charge distribution and discuss cluster stability.

Main Methods:

• Global structure exploration using parallel tempering Monte Carlo and local quenches.
• Potential energy calculations using density functional based tight binding (DFTB) for neutrals.
• Configuration interaction DFTB (CI-DFTB) for cations to account for charge resonance.
• Presentation and use of simplified DFTB schemes.

Main Results:

• Neutral pyrene clusters assemble into compact sub-units of up to three molecules.
• Cationic pyrene clusters exhibit a charged dimer or trimer core surrounded by neutral units.
• Structural analysis revealed correlations between cation features and charge distribution.
• Cohesive and evaporation energies were evaluated to discuss cluster stability.

Conclusions:

• Distinct structural motifs differentiate neutral and cationic pyrene clusters.
• The charged core in cationic clusters significantly influences their overall structure.
• The study provides insights into the stability and electronic properties of pyrene clusters.