水、甲醇和乙醇液体微结构性质的Car-Parrinello 分子动力学模拟

采用Car-Parrinello 分子动力学(CPMD)方法分别研究了水、甲醇和乙醇的液体微结构性质.研究结果显示:在水、甲醇和乙醇三个体系中O…O径向分布函数曲线的第一个峰位置分别为0.278、0.276 和0.275nm; O…H径向分布函数曲线的第一个峰位置分别为0.178、0.176和0.177 nm.表明基团(氢原子、甲基、乙基)的差异对O…O第一个峰的位置影响很小.但基团的差异对径向分布函数峰高的影响却很显著,由水到乙醇第一个峰的高度逐渐变高.空间分布函数表明氧原子和氢原子在溶剂分子周围有取向地分布,这与径向分布函数所表现出尖锐的第一个峰相一致.氢键分布分析显示,水、甲醇和乙醇的平均氢键数分别为3.62、1.99 和1.87,表明水形成了网状氢键结构,而甲醇、乙醇形成链状氢键结构.

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…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…H 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.