The two objectives of this work are to look at the molecular level mixing in water-alcohol liquid mixtures and to determine how well the Effective Fragment Potential (EFP) method performs at describing small, heterogenous water-alcohol mixtures. In this work we look both at small clusters, size 2 – 24 molecules, as well as bulk mixtures, 64 or more molecules.

For small clusters (2 – 24 molecules), the molecular structure was studied using the EFP method and MP2. Extensive Monte Carlo/simulated annealing (MC/SA) global optimizations were used to locate low energy structures for all water, alcohol, and water-alcohol mixtures. The alcohols studied include the small, straight-chain, primary alcohols: methanol, ethanol, propanol, and 1-butanol as well as the secondary alcohol 2-butanol, and tertiary butanol. It is shown that a number of low energy mixed clusters retain the structural characteristics of the pure clusters. It is also shown that the EFP method performs well at describing small, heterogenous water-alcohol mixtures.

The molecular structure in bulk water, alcohol, and water-alcohol mixtures is studied with the EFP method and molecular dynamics simulations. Radial distribution functions are used to analyze structure and to benchmark the EFP method against experimental results. The effect of alcohol concentration and alcohol chain length on the local structure of water is investigated. Preliminary results indicate that the EFP method can potentially model bulk water-alcohol systems well as compared to experiment. Results on the effects of alcohol concentration and alcohol chain length are forthcoming.