Communication: Benzene dimer--the free energy landscape

Area of Science:

• Computational chemistry
• Physical chemistry
• Molecular dynamics

Background:

• The relative orientation of molecules in dimers, such as the benzene dimer, is crucial for understanding intermolecular interactions.
• Previous studies suggest competing structures like T-shape and parallel displaced arrangements, with minimal energy differences complicating identification of the global minimum.

Purpose of the Study:

• To determine the most stable structure of the benzene dimer by calculating its free-energy landscape.
• To resolve the ambiguity between T-shape and parallel displaced structures.

Main Methods:

• Utilizing ab initio Car-Parrinello Molecular Dynamics.
• Employing metadynamics to compute the free-energy landscape of the benzene dimer.

Main Results:

• Calculations indicate that while competing structures can be energetically similar, the free energy landscape consistently favors a tilted T-shape geometry.
• This favored geometry is observed across all temperatures where the benzene dimer remains bound.

Conclusions:

• The tilted T-shape geometry is the thermodynamically preferred structure for the benzene dimer.
• Free energy calculations provide a more robust method than simple energy differences for determining the global minimum structure of molecular dimers.