Car-Parrinello Molecular Dynamics Simulations of Microstructure Properties of Liquid Water, Methanol and Ethanol

Car-Parrinello molecular dynamics (CPMD) calculations were performed on the solvent structure properties of water, methanol, and ethanol. The results show that the first O center dot center dot center dot O peaks of the radial distribution functions (RDFs) in the three systems are 0.278 nm for water, 0.276 nm for methanol, and 0.275 nm for ethanol. The first O center dot center dot center dot O peaks of the radial distribution functions (RDFs) in the three systems are at 0.178 nm for water, 0.176 nm for methanol, and 0.177 nm for ethanol. This indicates that the hydrophobic groupings (hydrogen, methyl, and ethyl) have little influence on the first peak position. However, the intensity of the RDFs increases from water to methanol and ethanol. The spatial distribution functions show that the oxygen and hydrogen atoms of other solvent molecules have characteristic orientations on the reference molecules in these systems. The results are in agreement with the first sharp peak of the radial distribution functions. We analyzed the hydrogen bonds using a statistical method. The results show that the average hydrogen bond numbers are 3.62 for water, 1.99 for methanol, and 1.87 for ethanol. Therefore, different hydrogen-bonded network structures are formed for liquid water, methanol, and ethanol via hydrogen bonds.