| Water, one of the most common substances on earth, is of tremendous importance for our daily life and many disciplines of science. Despite its simple molecular structure, water is very complicated and has many anomalies in condensed phases, mostly due to its vast and continuously changing hydrogen-bonding network. Experimentally, vibrational spectroscopy, especially in the OH bond stretch frequency region, is an ideal tool to investigate the microscopic structure and dynamics of this network. However, the interpretation of the experimental measurements usually needs the assistance of theoretical calculation. This thesis presents our recent work in simulating linear and non-linear vibrational spectroscopy of liquid water in diverse environments using a novel model. We believe our results provide new insights into this important and interesting field.;In this thesis, we use a newly developed water model, named E3B, which explicitly includes three-body interaction terms in its Hamiltonian. We begin with the simulation of the two-dimensional sum frequency generation spectroscopy at the water/vapor interface. The result reveals the slow hydrogen-bond switching dynamics at the water liquid/vapor interface. Then we evaluate the E3B model by comparing the temperature dependence of the theoretical non-linear vibrational spectra to experimental data. The result shows that the E3B model outperforms other commonly used models in terms of the microscopic dynamics of liquid water in a wide temperature range. Next, we propose a spectroscopic map for the water bend mode, and use it to study the vibrational spectra of this mode in the bulk liquid and the surface. The result has a reasonable agreement with the experimental data. We suggest that the bend mode, although studied less often than the OH-stretch mode, provides complementary information about the microscopic structure of water. At last, we discuss another interesting topic, which is the proposed liquid-liquid critical point of supercooled water. Using microseconds long simulation, we find evidence for the existence of a LLCP within the E3B model. We rationalize the result of our simulation by connecting this proposed critical point to the kink in the homogeneous nucleation line. |
