Modeling The Low Frequency Vibrational Spectroscopy Of The Ionic Solutions

This paper consists of seven chapters, the first four chapters for a wide range of basic knowledge and computing skills to pave the way for the theoretical sim-ulation of the spectrum. The first chapter briefly introduces the theoretical de-velopment of ionic aqueous solution and its important research prospects, the particularity of low frequency vibration spectrum and the significance of its ap-plication in ionic aqueous solution. Chapter 2 introduces the basis of molecular dynamics and its statistical mechanics. Chapter 3 focuses on quantum dynamics and one field of application is the nonlinear spectroscopy of Chapter 4.The molecular dynamics simulation of the second chapter is based on the classical mechanical equation of motion and the molecular mechanics model, and the equilibrium mechanics principle is applied to the adiabatic process of macro-molecules and relative long time scales. This chapter provides an overview of the basic elements of molecular dynamics such as empirical field, kinetic equation and simulation techniques. Although the accuracy of molecular dynamics is less than that of quantum chemistry, the significance of statistical mechanics is clear.Molecular dynamics simulation in the current computer performance rising back-ground, not only to explain the experimental phenomenon, and will play a key role in guiding experimental research.Due to the wide range of quantum dynamics, from quantum optics, solid physics to mathematical physics and many other scientific research. The third chapter only introduces the dynamic basis of Liouville space and the concept of correlation function. Then, a one-dimensional infrared spectroscopy is presented as an example of quantum dynamics to illustrate quantum dynamics and cor-relation functions. Chapter 4 briefly introduces the phenomenon and principle of nonlinear spectroscopy. Combined with the quantum kinetic calculation, the polarized intensity P of the material under strong laser field can be obtained.The nonlinear component, has a nonvolatile characteristic component p(n) and its coefficient is defined as the nonlinear polarization. When the assumed beam is pulsed, the nonlinear polarization is proportional to the corresponding higher order spectral response function. And the response function of the many projects,so you can draw the Feynmann diagram or Liouville space to distinguish them.In addition, the phase-matching motion equation as a non-perturbative method can greatly simplify the spectral calculation.The latter three chapters are theoretical simulation and analysis of the low-frequency one-dimensional and two-dimensional vibrational spectra of a series of ionic aque-ous solutions. Chapter 5 Combining different low-frequency spectra usually re-veals the mechanism of solution dynamics more clearly. Since OKE and DRS measure translation and rotation, this phenomenon is considered to reflect the glass-state characteristics of translational and rotational coupling. Our theoreti-cal simulation And the concentration dependence of the relaxation time reflects the hydrodynamic difference inside and outside the cationic hydrate shell, rather than the translational rotation separation. Dielectric relaxation spectra, the fit-ted peaks are in good agreement with the experiments. The next step is how to analyze this large number of trajectories to dig low-frequency shoulder fronts(about 0.5GHz) at the micro-origin.In chapter 6, the 2D Raman-THz spectra of different ionic aqueous solutions were simulated by the stability matrix method. The stability matrix method is based on the equilibrium state statistical mechanics principle and contains many information about the phase space. In order to consider the polarization effect of the ion, we introduce the dipole-induced dipole mechanism to calculate the total dipole and total polarizability of the trajectories of the molecular dynamics. The low-frequency spectrum requires a longer time-domain information span, so that the sampling points required for signal convergence are far beyond the ordinary spectrum. The low-frequency aqueous solution reflects the intermolecular degree of freedom movement pattern, and the thermal disturbance at room tempera-ture can be excited to the vibrational state. So the low-frequency spectrum of the ionic aqueous solution is very susceptible to the dissipation of environmental fluctuations.In the Brownian oscillator (BO) model, the different time series (RTT, TRT,TTR) of the 2D Raman-THz spectra of pure water can be qualitatively simulated using the dissipative sub-motion equation (DEOM). We turn the hydrogen bonds of the water 60 cm-1, the hydrogen bonds of 200 cm-1, the molecular swing 600 cm-1 model as a system, and other rapid local vibration separation, as the envi-ronment of the thermal rise drop. We divided the three low-frequency collective motion of water into two kinds, one with a strong dipole moment and environmen-tal disturbance, the relative frequency is higher; the other has a certain central symmetry, not susceptible to disturbance and damage Out. The former is mainly the swing of water molecules, while the latter belongs to the collective movement of hydrogen bonds.Conclusions and prospects: Molecular Dynamics Simulation Spectroscopy The current use of the ion nonpolarization Imodel is to matching with existing nonpolarized water models. With the recent new polarimetric field model (such as POLIR, POLI2VS, TTM3-F) is widely used, there will be matching with the ion non-polarization model, the polarization effect of real-time introduction to molec-ular dynamics simulation. For very low frequency GHz spectra, the development of large-scale trajectory conformational analysis techniques to the low frequency peaks corresponds to the kinetics. The theoretical simulation and experimental results of the 2D Raman-THz spectra are not currently consistent. And the abso-lute convergence of the time domain is still difficult, these problems can refer to Wolfgang Domcke proposed non-perturbative spectroscopy simulation method to overcome. Finally, the development of high efficiency for multi-mode BO model to improve DEOM simulation of 2D Raman-THz spectrum accuracy.