Computational Research On Vibrational Spectrum Control And System Energy Of Nano-scale Imidazole Ionic Liquids By Alternating Electric Field

The influence of changes in the external electromagnetic environment on the vibrational spectra of nanoscale ionic liquids is of great scientific significance and application value for understanding the internal bonding effects of ionic liquids and the dynamic changes of ionic interactions in electromagnetic fields.In this paper,a cubic simulation box containing 256 pairs of ions is established for imidazole ionic liquids 1-ethyl-3-methylimidazole hexafluorophosphate（[Emim][PF₆]）.A modified force field model was selected to construct the molecular dynamics calculation system.The DL＿POLY 4.09 software is used to perform molecular dynamics calculations on the system.After the equilibrium of the isothermal and pressure ensemble（NPT）and the regular ensemble（NVT）,the calculation system converges to a cube box with a side length of 4.237 nm.Then,the dynamic process of the alternating electric field of different amplitudes and frequencies is calculated.All of the calculations in parallel use multiple nodes configured with 187 GB memory and 40-core Intel Xeon Gold6248 chip.The calculation method of vibrational spectrum of the small non-equilibrium molecular dynamics system is transferred to the larger system of equilibrium molecular dynamics.And the vibration spectra of the nano-scale ionic liquids[Emim][PF₆]under the alternating electric field with a frequency of 0-250GHz and an amplitude of 0-5 V/nm are calculated.The vibration spectrum is divided into 5 frequency bands:terahertz frequency band,300-750 cm^-1 frequency band,750-1300 cm^-1 frequency band,1300-1650 cm^-1 frequency band,and 1650-3500 cm^-1frequency band.In each frequency band,by analyzing the intensity change and frequency drift of each vibration peak,combined with the calculation results of density functional theory,the relationship between the intensity change of vibration peak and the intensity change of functional group vibration mode,the response of vibration peak frequency drift and vibration mode to weak interaction such as hydrogen bond is correlated respectively,and the regulation mechanism of alternating electric field on ionic liquid is obtained.In addition,the phenomenon of spectral line interleaving and delamination in the vibration spectrum with the change of amplitude and frequency of alternating electric field is found.In this paper,the nonlinear regression analysis method is used to quantitatively study the relationship between both amplitude and frequency of the alternating electric field and the normalized intensity of the vibration peak.The classification expressions of two relations are obtained:the classification expression of the relationship between alternating electric field amplitude and vibration peak normalization intensity fitted by Lorentz function,and the classification expression of the relationship between alternating electric field frequency and vibration peak normalization intensity fitted by Gaussian function.It is found that the change rate of the normalized intensity of the vibration peak varies with the increase of the amplitude and frequency of the alternating electric field.And important conclusions are obtained.For instance,the normalized intensity change rate of the higher intensity and high-frequency vibration peak is larger.In order to reveal the hysteresis of the dynamic characteristics of the ionic liquid computing system on the response when the frequency of the alternating electric field increases,this paper also studies the influence of the frequency of the alternating electric field on the energy of the system.The amplitude of the alternating electric field is constant at 2 V/nm,and the frequency range is 0-200 GHz,the configuration energy,electrostatic energy,bond stretching potential energy,bond angle bending potential energy,and dihedral torsion energy of the ionic liquid nano-scale system are calculated.It is found that when the frequency of the alternating electric field increases,the periodic fluctuation of the energy curve of configuration energy and electrostatic energy will lag behind.The above research results provide a scientific basis for the application of nano-scale imidazole ionic liquids in electromagnetic environments.