| Poly（ionic liquid）s（PILs）are composed of the chain of anions or cations in ionic liquids（ILs）and counter ions,because the structure of PILs are similar to ILs system,PILs also have many of the same advantages as ILs and are even better.For example,PILs have better chemical stability,thermal stability and higher ionic conductivity and currently have been widely used in the field of electrolyte and new materials.However,at present,most of the PILs systems are studied by experimental methods,there are few theoretical studies on microscopic mechanism.Different selection and combination of PILs will produce different properties.Therefore,the molecular dynamics simulation is used to simulate different PILs systems to explore microscopic mechanism,save the cost of experimental search,and provide theoretical guidance for the selection and design.Molecular dynamics（MD）simulation is one of the best methods to study the microscopic mechanism.However,the PILs have polymer chain structure,which makes it difficult to realize long-term and large-scale simulations,and the calculation cost is expensive.Therefore,this work establishes a coarse-grained（CG）model of PILs by referring to the simulation methods of ILs and polymers.In this work,we used the Boltzmann Inversion（BI）method to obtain bonded potential for ploy（1-vinyl-3-ethylimidazolium tetrafluoroborate）[PVEIm][BF4]CG model,and obtained non-bonded potential parameters by using Iterative Boltzmann Inversion（IBI）method.In order to complete the iterative process more efficiently,the Python language and the Linux system were used to automatic iterative process to obtain non-bonding potential parameters.After a long iteration until the error is within the acceptable range.The structural accuracy of the CG model was verified by comparing the bond and angle distribution between the all-atom（AA）and CG system.By comparing the density with the glass transition temperature,the density error is within 5%at the temperature of 298K.In addition,Table potential method and L-J parameters methods were used to represent the non-bonded parameters to calculate the self-diffusion coefficients respectively,and the advantages and disadvantages of the two methods were compared.The conclusion obtained from the analysis results are:（1）the bonded parameters for CG model obtained by BI method can well restore the structural properties of polymer chain;（2）Table potential to represent non-bonded parameters,the structural properties between anions and cations can be well restored;（3）the L-J parameter method to represent the non-bonded parameters can well rebuild the dynamics properties.The study in this work can provide a theoretical basis for the simulation of PILs systems in the future.In the future researches on the CG model of PILs,different method of non-bonded parameters can be selected according to different research purposes. |
