Molecular Dynamics Simulation On The Potential Of Mean Force Of Ionic Liquid [Bmim]Cl In The Water

The Ionic liquid (IL) takes as a new "the green resolver", in recent years, which caused wide attention to the related scholars in various countries, especially in the chemical fields. The variety of ILs is great. Moreover, their properties may be designed according to our need through changing the combination way of cations and anions. But, in the practical application process, we cannot screen ILs completely depending on the experiments, which will cost many time and expense. Therefore, we combine molecular dynamics simulation and the theory to investigate free energy (Potential of mean force, PMF) of mixtures of ILs/water. We analyse the interactions of anion-water, cation-water through their microscopic structures. And we studied influence of the interactions to the potential of mean force, simultaneously, carried on the comparison with the ion solution. First, in the second generation of AMBER force field, we carried out molecular dynamics simulation on PMF of mixtures of methane /water, which checked the realization of the umbrella sampling method and WHAM method, and optimized the parameters through the fitting method. This work simplified simulation process. We also calculated PMF and radial distribution function of a series of mixtures of NaCl /water with different charge quantity. Through the comparison, we discovered that different charge quantity of anion and cation influence PMF and the microscopic structure remarkablely. Based on this, we studied PMF of [bmim]Cl in vacuum, and by tracking cation and anion, we discovered that they separated in the initial simulation and separated very far. Then, we studied PMF of mixtures of [bmim]Cl/water with molecular dynamics simulation. Results showed that the interaction of cation and anion with water affected PMF of ILs. Simultaneously, we carried on the comparison with PMF of ion solution NaCl. Results showed that the changing of cation leads to the difference of PMF. We analyzed the microscopic structure of IL and ion solution through radial distribution functions of anion-water and cation-water. In summary, molecular dynamic simulation and theory are combined to investigate the PMF and radial distribution functions of ion solution NaCl and the mixtures of [bmim]Cl/water. The comparison results in this work, reflecting energy-structure relationship the in the systems, are helpful in screening ILs.