On the composition dependence of thermodynamic, dynamic and dielectric properties of water-methanol model mixtures. Molecular dynamics simulation results

TL;DR

This study uses molecular dynamics simulations to analyze how thermodynamic, dynamic, and dielectric properties of water-methanol mixtures depend on composition, highlighting the need for improved methanol models for better accuracy.

Contribution

It provides a comprehensive simulation-based analysis of water-methanol mixtures across all compositions, linking hydrogen bonding to macroscopic properties and suggesting model improvements.

Findings

Hydrogen bonding patterns correlate with mixing volume and enthalpy.

Current models can be improved with more sophisticated methanol representations.

Force field parametrization impacts mixture property predictions.

Abstract

We have investigated thermodynamic and dynamic properties as well as the dielectric constant of water-metha\-nol model mixtures in the entire range of composition by using constant pressure molecular dynamics simulations at ambient conditions. The SPC/E and TIP4P/Ew water models are used in combination with the OPLS united atom modelling for methanol. Changes of the average number of hydrogen bonds between particles of different species and of the fractions of differently bonded molecules are put in correspondence with the behavior of excess mixing volume and enthalpy, of self-diffusion coefficients and rotational relaxation times. From the detailed analyses of the results obtained in this work, we conclude that an improvement of the description of an ample set of properties of water-methanol mixtures can possibly be reached, if a more sophisticated, carefully parameterized, e.g., all atom, model for methanol is used. Moreover, exploration of parametrization of the methanol force field, with simultaneous application of different combination rules for methanol-water cross interactions, is required.