Ethylene glycol revisited: Molecular dynamics simulations and visualization of the liquid and its hydrogen-bond network ^☆

Abstract

Molecular dynamics simulations of liquid ethylene glycol described by the OPLS-AA force field were performed to gain insight into its hydrogen-bond structure. We use the population correlation function as a statistical measure for the hydrogen-bond lifetime. In an attempt to understand the complicated hydrogen-bonding, we developed new molecular visualization tools within the Vish Visualization shell and used it to visualize the life of each individual hydrogen-bond. With this tool hydrogen-bond formation and breaking as well as clustering and chain formation in hydrogen-bonded liquids can be observed directly. Liquid ethylene glycol at room temperature does not show significant clustering or chain building. The hydrogen-bonds break often due to the rotational and vibrational motions of the molecules leading to an H-bond half-life time of approximately 1.5 ps. However, most of the H-bonds are reformed again so that after 50 ps only 40% of these H-bonds are irreversibly broken due to diffusional motion. This hydrogen-bond half-life time due to diffusional motion is 80.3 ps. The work was preceded by a careful check of various OPLS-based force fields used in the literature. It was found that they lead to quite different angular and H-bond distributions.

Graphical abstract

Highlights

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  We simulated liquid ethylene glycol classically.

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  Four OPLS-AA based force fields were compared.

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  Hydrogen bonds were identified by geometrical criteria.

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  Lifetimes of hydrogen bonds were obtained using the population correlation formalism.

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  A visualization of individual hydrogen-bond lifetimes was implemented and clustering of hydrogen bonds was observed.