MD Simulations On The Interfacial Structure Changes Between Ice And Water

Icing phenomenon exists widely in nature,which brings great inconvenience to production and life,such as reducing the operating efficiency of equipment,leading to safety risks and even disasters.Although the formation of ice crystals is closely related to human life,the molecular mechanism of the formation of ice crystals is poorly understood.The ice-water interface is the frontier of phase transition,water molecules at the interface reversibly transform between disordered and crystalline states,so the interface structure fluctuates.These fluctuations have important effects on the stability of ice nuclei and the structural evolution of ice crystals.At the same time,it is very important to understand and master the evolution law and regulation of ice-water interface.During recent years,extensive and in-depth theoretical research has been carried out on the interface structure by computer simulation.To study the dynamic process of the ice-water interface structure,a model of ice-water coexistence was established in a microcanonical ensemble(NVE)to reveal the dynamic change process of the ice-water interface microstructure and its regulation rules.The main findings and achievements are shown as followsFirstly,the solid-liquid coexistence method was used to determine the melting point of the water model to obtain the environmental parameters such as pressure and temperature in the equilibrium state,and the calculated results were consistent with those obtained by the volume-temperature phase diagram.However,the calculation amount of the solid-liquid coexistence method was smaller.At the same time,the influence of size effect on the simulation results was also verified.In the system with larger size,the fluctuation of thermodynamic parameters was more gentle,and the calculated values were more accurate.In different simulation environments,the influence of the fluctuation law on the ice-water interface on the process of the crystallization and melting has been studied.Secondly,an ice-water model was established to simulate the dynamic process of the ice-water interface structure.The simulation results showed that ice growth occurred by reorganization of the hydrogen-bonded network near the interface.when the two phases coexisted,the generation and fracture of hydrogen bonds occurred in the interfacial layer at the same time.So disordered liquid water molecules and ordered ice crystal structure existed in the interfacial layer.It was also found that the interface for the basal plane had a molecularly flat structure and the rearrangement of the hydrogen-bonded network occurred two-dimensionally,whereas the interfaces for the prismatic plane and the secondary prismatic plane had a geometrically rough structure and the rearrangement of the hydrogen-bonded network occurred three-dimensionally,which elucidated the anisotropy of the interfacial structure during the growth of solid-liquid systems on the molecular scale.The liquid layer thickness was found to decrease when the temperature was lower than the melting point.Furthermore,the influence of temperature on the motion of water molecules in the interfacial layer was explained from the view of "the competition and compromise between dominant mechanisms".The order parameter was used to characterize the structural change of the system.With the coexistence of two phases as the initial state,higher energy was obtained to break through the lattice constraints for the water molecules when the temperature increased,which demonstrated that the melting process of ice crystals played a dominant role.With the decrease of temperature,the degree of supercooling increases,the driving force of crystallization increases,and the free energy barrier decreases,so that the ice crystal growth plays a dominant role.This research will gain a deeper understanding of the formation mechanism of dynamic structure,and provide a new thought for the study of complex interfacial structures during phase transition.