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The ionic liquid is only constituted by the anion and cation , a new type of organic solvent is still liquid at room temperature , because it almost non-volatile, be regarded as a \In recent years , the unique nature aroused extensive attention of scholars from various countries of the world , especially in the field of chemical engineering , is expected to replace traditional volatile organic solvents in many chemical processes , and to contribute to improve the deteriorating environment . More importantly , by changing the combination of the anions and cations according to the need to design their nature . But in the practical application of the process is neither necessary nor possible to completely rely on experiments to complete the screening to spend a lot of time and expense . Therefore , the use of molecular simulation methods to study the relationship of the structure and characteristics of ionic liquids at the molecular level , is of great significance . In this study, a focus on the ionic liquid in water mean force potential (Potential of Mean Force, referred PMF), supplemented by local microstructure analysis , the potential energy function by changing the purpose of the simulation study its impact on the average potential energy to . First of all, we methane molecules in water PMF molecular dynamics simulations , for example, umbrella sampling (Umbrella Sampling) and WHAM (Weighted Histogram Analysis Method) method to calculate the average force potential , and details of the calculations and parameter optimization discussed. Secondly, the study of NaCl in water PMF analyzes used to characterize partial micro - structure of the radial distribution function ; addition, by changing the ionic charge in the simulation , it is found to have a significant effect of potential energy function of the PMF and microstructure . On this basis , preliminary exploration of the ionic liquid [bmim] Cl anions and cations in water PMF found in water interaction is significantly less than the sodium - chloride ion pairs . Unlike aqueous NaCl , [ bmim] Cl in the water to contact ion pairs present in the form probability far less than the sodium - chloride ion pair, this because [bmim] cation asymmetric structure with sodium ion significantly different . In short , this work by comparing the ionic liquid and simple ion solution in water mean force potential energy , and to explore the mechanism on the microscopic point of view , and laid the foundation for the further study of ionic liquids with water or other intermolecular interactions , screening specific functions the ionic liquid played a certain role of guidance and reference .
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