MONTE-CARLO SIMULATION OF WATER-TETRAHYDROFURAN MIXTURES

Monte Carlo simulations of water-tetrahydrofuran (THF) mixtures were p erformed in the isothermal-isobaric ensemble (NPT) at T = 298 K and p = 1 atm. The interaction energy was calculated using the TIP4P model f or water and a five-site united atom representation for the THF molecu le. The potential energy surfaces for water-THF interactions were obta ined by using combining rules and the original potential functions use d for pure liquids. Theoretical values obtained for the average intera ction energy as a function of concentration are in good agreement with available experimental data. Results from the partitioning of the tot al interaction energy into water-water, water-THF and THF-THF contribu tions are presented. These results are useful to distinguish between t he quantitative contributions of these molecular interactions to the e nergetic behavior of the water-THF mixing process: The radial distribu tion functions for H-W-O-THF and O-W-O-THF site-site interactions show the salient features of hydrogen-bonded liquids. Comparison of the av erage number of water-water complexes interacting through hydrogen bon ding in water-THF and water-methanol mixtures shows an enhancement of the water-water coordination number in a THF rich environment.