First-Principles Study Of Monolayer Ice Structure

Water/ice is extremely abundant on earth,which is also one of the substances with the largest number of anomalies in its properties.These unique properties play an important role in many natural phenomena and processes,while many of their mechanisms are still unknown.In contrast,at the microscopic scale,water has a relatively simple molecular structure.These seemingly contradictory performances can be largely attributed to the hydrogen bonding between water molecules.The hydrogen bonding is related to a large amount of characteristics of water and ice.When entering the two-dimensional level,the dimension reduction provides additional degrees of freedom and the structural diversity of ice is further improved.Twodimensional(2D)ice or water exists widely in nature,such as on the surface of rock or metal and in slit pores between 2D materials.Therefore,it is of importance to grasp the intrinsic factors that determine the structure and dynamics of the low-dimensional ice.It helps to discover the unique phenomena of low-dimensional systems,which at the same time is conducive to our understanding of bulk ice.In this thesis,a systematic study of monolayer ice is carried out based on the density functional theory.We focus on it from three aspects:the first is the competition between water-water and water-substrate interaction;the second is the disorder of hydrogen atoms in monolayer ice and the related structural and dynamic properties;the third is the comparison between 2D and bulk ice,and distinguishing the characteristics of the 2D ice itself from the influence of the substrate.The specific research can be divided into the following parts:1.The monolayer ice adsorbed on the close-packed(111)surface of the noble metals gold,platinum,and palladium has been systematically studied by using the firstprinciples calculation method.By analyzing a series of nearly degenerate structures,we reveal the structural diversity as an intrinsic property of the adsorbed monolayer ice,which helps to clarify the debate about the structure of such system.We propose a quantitative description of the complementary between water-water and water-metal interactions,which can be responsible for the structural diversity.2.The effect of the disorder of hydrogen atoms on the stability of monolayer ice adsorbed on the platinum(111)surface has been systematically studied by using the first-principles calculation method.We focused on two kinds of disorder phenomena,namely the dangling hydrogen disorder and water molecular arrangement disorder.And we reveal that the disorder does contribute to the stability of the adsorption,which can provide favorable evidence for the existence of disorder in two-dimensional ice.From the view of water-water and water-metal interactions,we also analyze the reason why disorder affects the stability.3.The ab initio molecular dynamics method has been used to study the thermodynamics and kinetics of the monolayer ice adsorbed on a metal surface at finite temperature.The phenomena of water molecules flipping and hydrogen atoms rearrangement at relatively low temperatures are proposed.On this basis,we point out for the first time that the state of the adsorbed monolayer ice between absolute zero and room temperature can be divided into four stable phases:ordered at low temperature-disordered at low temperature-ordered at high temperature-disordered at high temperature.It is revealed that the source of this phenomenon is the unique condition of the surface.We also make a brief comparison with the disordered premelting of the bulk ice surface.4.The structure and stability of free-standing monolayer ice with different pattern(such as hexagonal,square,etc.)has been studied by using the first-principles calculation method.We reveal the factors that determine the stability,as well as the relation between them.The role of strain are also studied.We also analyze the effect of different kinds of disorder phenomena on the structure and stability of free-standing monolayer ice.Subsequently,we compare the above situation with that in surface adsorption,to distinguish the characteristics of the 2D ice itself from the influence of the substrate.