| Liquid materials with very good mechanical properties and non-linear effect, have been widely used in photoelectric device, such as liquid-core optical fiber and optofluidic. Imidazolium ionic liquids are a new type of green liquid materials. And we can select or change anion, cation and the length of alkyl substituent to achieve the designable to a certain extent, and finally control the nonlinear polarizability. In this paper, using numerical calculation, we explore and study the nonlinear optical properties of imidazolium ionic liquids applied by electric field.First of all, based on the principle of molecular dynamics, combining with the physical properties of ionic liquids, we build the single molecular model of imidazolium ionic liquid-[EMIm]NO3. And through the Gaussian software, the single molecule model is optimized.Then extending the single molecule model to512molecules mixed system by programming, using both the NVP and NPT ensemble molecular dynamics calculations, make the whole system properly balanced. And the densities of the [EMIm]NO3both theoretical and experimental reach a constant. Then we get the non-equilibrium state of ionic liquids by adding an external electric field in the X direction by molecular dynamics simulation. Combining with nonlinear optics, the nonlinear polarizability of the ionic liquid system is calculated. And then we get polarization of the molecular mixing system by changing the intensity of the field repeatedly. Finally we get the first-order and third-order nonlinear optical susceptibility of [EMIm]NO3by polynomial fitting. The study results indicate that polarizability with simulation and experiment are consistent, verifying the correctness of our study.This paper establishes a multi-molecular system model of imidazolium ionic liquids, and calculates the nonlinear polarizability under the electric field. And our study will enhance the development of ionic liquids in the nonlinear field. |
