First-Principles Studies Of Aerosol Nucleation And Nanowire Growth

Chemistry has always been known to the public as an experimental science.From the establishment of quantum mechanics,solving wave function,to the establishment of density functional theory,along with the development of computer technology,computational chemistry has been booming.First-principles study on microscopic systems has become an indispensable means of research involving physics,chemistry,materials science and so on.The study of nucleation and growth mechanism is of great significance for understanding the formation mechanism of gaseous particles and nanomaterials.In this paper,the application of first principles to the nucleation of aerosol clusters and the morphology control mechanism of one dimensional nanowires are discussed in detail.The first chapter introduces the theoretical methods involved in the this dissertation.An introduction to density functional theory and cluster search algorithms is included.In chapter two,the background of aerosol nucleation and the existing research are reviewed.Aerosols affect air quality,human health,ecosystems and even weather and climate.Primary aerosols are directly discharged into the air by nature or human,and secondary aerosols are generated through different physical and chemical pathways,which are considered to be the main source of aerosol particulate matter.People's research on secondary aerosol is divided into field measurement,laboratory instrument exploration,theory and model research.For a long time,low volatile substances have been considered to be the key to aerosol nucleation,such as sulfuric acid,iodine oxide and low volatile organic matter.With the development of economy,urban environmental pollution has greatly affected the normal activities of human beings.The complexity of urban pollutants and the environment makes it impossible for previous studies to explain the new particle nucleation phenomenon in cities.In recent years,with the improvement of industrial desulfurization technology and the improvement of emission standards,the content of SO2 has gradually decreased,but the emission of NOx has continuously increased,and the proportion of nitrate in urban haze has continuously increased.The latest study on nucleation of nitric acid and ammonia gas system shows that the saturation ratio of ammonium nitrate is the thermodynamic driving force of condensation.In chapter 3 and chapter 4,aerosol nucleation with nitric acid and ammonia as the representative is studied by first principles.For nitric acid-ammonia systems,containing four nitric acids and four ammonias are calculated.There are a lot of water molecules in the atmosphere,,the water cluster of nucleating material is studied to obtain more accurate evaporation coefficient under different relative humidity using electronic structure calculation,so as to more accurately simulate the formation rate and growth path.A more profound understanding of the nucleation process will be revealed.In our work,we calculated the number of water molecules contained in the hydrate as 5?13 to achieve convergence.The results obtained provide a more accurate description on nucleation at different relative humidity especially high relative humidity.Based on the lowest energy structures,a series of data analysis was performed,including hydration distribution,collision coefficient.The evaporation coefficient is the parameter that can most directly reflect the cluster growth situation.The analyzed results reflect the sensitivity of humidity to cluster evaporation rate and its effect on partial evaporation paths.The formation rate and growth path obtained by our further simulation revealed that the formation rate is greatly enhanced under the conditions of higher pollutant concentration,lower temperature and higher relative humidity(RH).Nucleation mechanism also changes with the change of initial concentration of HNO3,NH3,temperature and relative humidity.The nucleation mechanism reflected by growth path also changed.In chapter 5,the experimental cooperation group controlled the ratio of organic surfactants PVP(polyvinylpyrrolidone)and CPK(cyclopentanone),which could accurately modulate the growth of Te/Pd nanowires,and the microscopic explanation is given by using first-principles calculation and exploration.We simulated the binding energy of 2-pyrrolidone(2P)and CPK on the specific crystal plane of Te/Pd.Through calculation and test,it was found that the oxygen in these molecular structures had the strongest interaction with the surface.The model was established based on the adsorption of oxygen at specific sites to find the lowest configuration and calculate the corresponding binding energy.The internal mechanism of modulating growth is that the binding energy of different molecules on different surfaces is different,so controlling the proportion of surfactant can accurately regulate the morphology of nanowires.