Dynamic simulation of liquid molecular nanoclusters: structure, stability and quantification of internal (pseudo)symmetries

Abstract

The atom–atom intermolecular force field AA-CLP is applied to the molecular dynamics simulation of liquid nanoclusters of benzene, chloroform, methanol and pyridine. Bulk liquids are also simulated for validation and comparison with experimental data. The applied software has been produced de novo to deal with the unusual analytical form of the intermolecular potential, and it includes some novel features for the control of net rotational momenta in isolated systems. The nanoclusters have been studied as a function of size (150–1000 molecules) in relation to cohesion energies, rotational correlation, self-diffusion coefficients, and evaporation rates. Internal structure has been studied with traditional radial distribution functions, plus diagrams of the distribution of intermolecular vectors for flat compounds. In addition, a new algorithm for the quantification of pseudo- or near-symmetries between molecules in aggregates of any structure has been developed and tested, with reference to the inversion, mirror plane and rotation axis symmetries of organic crystals, with possible importance in the investigation of crystallization processes. The results confirm the reliability of the AA-CLP formulation for molecular dynamics simulation and throw some light on relationships between cluster and bulk properties. The computer codes are available for open-source download to ensure full reproducibility of all results.