Coarse-grained Model For Ionic Liquids Based On K-means Algorithm

Ionic liquids(ILs)as a new class of green organic solvent composed of anions and cations,as liquid at room temperature.It has unique properties,such as low melting point,low vapor pressure,adjustable structures,etc.In recent years,it has been widely used in catalysis,separation,materials science,life science and other fields.It is extremely important to study the mechanism of ionic liquid intermolecular interaction.It's significant to study the relationship between structure and property at the molecular level by molecular simulation.In this process,it is necessary to establish a reasonable force field model for the ionic liquid and to study the relationship between the structure and the property of the ionic liquid.We should to select the appropriate algorithm to improve the computational efficiency,to achieve large-scale simulation study.As a classical algorithm in clustering analysis,K-means clustering algorithm can divide the samples into several clusters,so that the samples in the same cluster have high similarity,and the samples in different clusters are highly different and widely used in large data processing,gene recognition,image processing and other different areas.In this paper,based on the K-means algorithm in data mining,the molecular dynamics of 5000 pairs of [Cnmim][Cl](n = 4,6,8)ionic liquids and 150 pairs of [Cnmim][Cl](n = 4,6,8,10,12,14)ionic liquids systems were simulated.And then the radial distribution function of the all atom force field was fitted to obtain the table potential energy of the coarse-grained model.The coarse-grained model I and coarse-grained model II are established based on these table potential energy.In order to verify the precision for two kinds of coarse grained models,density,thermal expansion coefficient,self diffusion coefficient,mean square displacement and conductivity properties are calculated by using molecular dynamics method compared with the result of all atom force field.The results are good agreement with all atom force field simulation.In addition,in the same simulation conditions the simulation time can be analyzed,we found that the efficiency of coarse grained model of I is better than that coarse grained model II,in addition the calculation speed of [C12mim][Cl] is increased by 23.98% than all atom simulation.The research in this paper provides a new method for the development of the ionic liquid coarse-grained models,provides a theoretical possibility for the simulation of the dynamic properties of the real ionic liquid system and provide a new idea for large scale calculation.