Equilibrium structures of anisometric, quadrupolar particles confined to a monolayer

TL;DR

This study explores the equilibrium structures of anisometric quadrupolar particles in a monolayer, revealing complex configurations and the stability of certain structures under thermal fluctuations, advancing understanding of molecular monolayer arrangements.

Contribution

It introduces a comprehensive analysis of ground state and thermal behavior of quadrupolar ellipsoidal particles, combining evolutionary algorithms and molecular dynamics simulations.

Findings

Complex ground state structures with multiple orientations were identified.

Particles with high aspect ratios maintain stability at elevated temperatures.

Thermal fluctuations influence the arrangement and stability of the structures.

Abstract

We investigate the structural properties of a two-dimensional system of ellipsoidal particles carrying a linear quadrupole moment in their center. These particles represent a simple model for a variety of uncharged, non-polar conjugated organic molecules. Using optimization tools based on ideas of Evolutionary Algorithms, we first examine the ground state structures as we vary the aspect ratio of the particles and the pressure. Interestingly, we find, besides the intuitively expected T-like configurations, a variety of complex structures, characterized with up to three different particle orientations. In an effort to explore the impact of thermal fluctuations, we perform constant-pressure Molecular Dynamics simulations within a range of rather low temperatures. We observe that ground state structures formed by particles with a large aspect ratio are in particular suited to withstand fluctuations up to rather high temperatures. Our comprehensive investigations allow for a deeper understanding of molecular or colloidal monolayer arrangements under the influence of a typical electrostatic interaction on a coarse-grained level.