Molecular dynamics of flexible molecules: torsional motions of n-butane and ethylene glycol

Molecular dynamics simulations have been performed for liquid n-butane and ethylene glycol (1,2-ethanediol; EG) in order to understand liquid structures in terms of both inter- and intra-molecular interactions. Each n-butane molecule consists of four sites interacting with LJ potential, and with only one dihedral angle potential, while each EG molecule has six sites interacting through LJ and coulomb potentials together with three dihedral angle potentials. The flexible molecule has the tendency to be folded more intensely in the liquid state than that in the gas phase. Comparing aqueous solution of EG with Xe solution and gaseous state of EG, it is found that EG molecules more strongly favor the folded form by intramolecular interactions, especially by intramolecular hydrogen bond.