AB Initio Molecular Dynamics Study Of The Hydrogen Bonding In Liquid Water

Water is not only a valuable natural resource, but also a necessary survival condition of human being. Water is ubiquitous and one of the most important liquids to investigate. Due to its critical role in many chemical and biological processes,a detailed understanding of the structural and dynamical properties of water is essential.The properties of water are dominated by its ability to form hydrogen bond networks. The networks are dynamic, with the strengths and numbers of hydrogen bonds associated with a particular water molecule constantly fluctuating. It is generally accepted that the distinctive properties of water can be ascribed to hydrogen bonding.The fundamental dynamical processes of the liquid is the forming and breaking of hydrogen bonds. This dynamics, however, is far from being completely understood!Experiments such as infrared absorption and Raman scattering, depolarized light scattering, and inelastic neutron scattering can only probe hydrogen bond dynamics indirectly and be interpreted in a qualitative way. Experimental techniques to determine the structure of liquid water are lacking since each water molecule undergoing rapid rearrangement on the order of femto-seconds. The need for a better understanding of water at the microscopic level has forced the development of computational methods that describe the structure and dynamics of individual water molecules, and many studies have been carried out using these techniques.Now, Car-Parrinello molecular dynamics (CPMD) has become the most important ab initio molecular dynamics method based on the first principle theory. In this paper, we carried out studies of liquid water with CPMD computational methods to study the properties of liquid water which related to the hydrogen bonds.Through statistical analysis of the simulation results of liquid water, we get the radial distribution function, the orientational distribution function, the rate of H-bonds and the lifetime of H-bonds. From these data the following conclusions are:1. In liquid water,more water molecules are tetrahedraly coordinated with four water molecules of the first solvation shell through hydrogen bonds in the form of dimmer;2. As the increase of temperature, the rate of the H-bonds decrease;3. the H-bonds lifetime in liquid water vary from 200fs to 100fs. The lifetime of non-H-bonds in liquid water is under 100fs.This paper also presented that temperature is the main factor affecting hydrogen bonds, the higher the temperature the more intense thermal motion of water molecules, Thereby speeding up the relaxation process of the H-bonds structure.Through the research and analysis of the system of water molecules we got some quantitative results. Gave us more profounding understands of the microscopic nature of the liquid water.