Local structure and hydrogen bonding in liquid γ-butyrolactone and propylene carbonate: A molecular dynamics simulation

Abstract

In this work we report a new potential model for classical molecular dynamics (MD) simulation of two dipolar aprotic solvents – propylene carbonate (PC) and γ-butyrolactone (GBL). Parameters for intramolecular interactions as well as the partial atomic charges were derived from quantum chemical calculations, while the OPLS/AA force field Lennard-Jones intermolecular parameters were adjusted to reproduce the experimental thermodynamic and the transport properties of these solvents in the wide temperature range. The comparison of new potential models with existing models for PC and GBL is given. Using the proposed models, the local structure of these solvents was studied in detail, paying special attention to packing ability, dipole-dipole orientation and hydrogen-bonding (H-bonding) interactions. Based on the results of MD simulations and QTAIM analysis, it was shown that H-bonds involving carbonyl oxygen atoms in PC and GBL are rather weak, while no H-bonds are formed with ester oxygen atoms. According to the present results, the mutual molecular orientation in PC and GBL varies with the distance, being above/below plane-parallel configuration for closest neighbors, and in-plane T-shaped configurations for farther neighbors. The nearest neighbors approach coupled with angular distribution functions was applied for the estimation of the Kirkwood factor in the framework of the Onsager-Kirkwood-Fröhlich theory. Our results shows that in order to reproduce the corresponding experimental values the Kirkwood factor it is necessary to take in account the mutual orientation of ~8–9 neighboring molecules for GBL and ~5–6 molecules for PC.