Akadēmiskais centrs
Water-methanol and water-ethanol liquid mixtures have been investigated by X-ray diffraction and molecular dynamics computer simulations over the entire concentration region at room temperature. It has been found that for ethanol-water mixtures, the combination of OPLS-AA potential for the alcohol and (depending on the composition) the SWM4-DP (polarizable) or the TIP4P/2005 (non-polarizable) water potentials provide nearly quantitative agreement with measured X-ray data. Agreement between simulation and experiment for water-methanol mixtures was still fair. Hydrogen bonding statistics (such the number of H-bonds/molecules, clustering, and even percolation over H-bonds) have been calculated from the simulated particle configurations.
For the water-rich compositions, literature X-ray data are available as a function of temperature. Molecular dynamics simulations for water-methanol mixtures, using the OPLS-AA alcohol and the SPC/E water potentials, were able to reproduce ll observable trends as the mixtures were cooled down to about 223 K. Analyses of H-bonded structures has been carried out. The most remarkable finding was that formation of 6-membered H-bonded rings has been enhanced greatly as the temperature approached the freezing point of the mixtures.