Functional Design And Excited Carrier Dynamics At Oxide Heterostructure

With the maturity of theoretical simulation methods and rapid development of computer technology,the first-principles calculation has become an essential scientific tool in various fields such as physics,chemistry and materials,due to its low cost,high efficiency and accuracy.In this thesis,we investigate the solvated electron states of LaAlO3/SrTiO3(LAO/STO)heterostructure,the photogenerated carrier dynamics at the anatase/rutile TiO2 interface,and the physical mechanism about K atom promotion of O2 chemsorption on Au(111)surface,by using the first-principles calculation,the adaptive genetic algorithm(AGA)method,and the non-adiabatic molecular dynamics(NAMD)method.In the first chapter,firstly,we briefly introduce different kinds of theoretical calculation methods for many-body system,and focus on the DFT calculations.Then,starting from the adiabatic molecular dynamics,considering the excited states where the adiabatic approximation no longer valid,we mainly introduce the NAMD method based on time-dependent density functional theory and surface-hopping.We also introduce the specific process of the excited state dynamics calculation for many-body system by using Hefei-NAMD code.Finally,we briefly introduce the global structure optimization algorithm,and focus on the AGA which combine the DFT and genetic algorithm,and also give the computational flow of the AGA method.In the second chapter,we introduce a theoretical design scheme for regulating the properties of solvated electron states through polar-nonpolar oxide heterostructure.Solvated electron states at the oxide/aqueous interface represent the lowest energy charge-transfer pathways due to its diffuse characteristics.When the electrons are excited into the solvated electron states,the proton-electron coupling charge transfer processes often occur,so there are many important applications in the fields of physics,chemistry and biology.However,the solvated electron is often difficult to be fully utilized due to its high energy and short lifetime.Taking LAO/STO heterostructure with H20-adsorbed monolayer as a prototypical system,we show using DFT simulation that the energy of solvated electrons can be tuned by the electric field in the polar-nonpolar oxide heterostructure,which will facilitate the application of the solvated electron states in photocatalytic reactions and charge transport.In addition,we also use NAMD method to simulate the charge transfer dynamics of the excited solvated electrons when the LAO is thinner than four unit cells in p-type LAO/STO heterostructure,which is very difficult to observe in the experiments.In the third chapter,we investigate the stable interface structures and electron-hole separation and electron-hole recombination dynamics of the anatase/rutile mixed-phase TiO2 by using AGA and NAMD methods.Then,with the presence of oxygen vacancies,we investigat the influence of defect states on the electron-hole recombination process in the TiO2 heterojunction.Finally,based on our calculation results,we summarize the general laws of charge transfer and electron-hole recombination dynamics in TiO2 heterojunctions,which may partially explain the longstanding controversy observed in different experiments.We propose that our study provides atomic insights into the understanding of the photogenerated carrier dynamics at the mixed anatase/rutile TiO2 heterojunction.which provide valuable guidance for functional material design for solar energy conversion.In the fourth chapter,collaborated with the experimental group of the University of Pittsburgh,we study the chemical coadsorption of K and O2 on the Au(111)surface at the atomic scale by scanning tunneling microscopy(STM)and DFT calculations.We find that decoration of the Au(111)surface with a K+ ion dipole superstructure remarkably increases the O2 chemisorption;this is enabled by decrease of the work function of the weakly physisorbing Au(111)surface,which facilitates the reduction of the gas phase O2,and thereby introducing anions to interact with the existing K+ cation lattice.Also,in combination with experimental statistical analysis and DFT calculations,the atomic scale structures of different coadsorption motifs are determined.Moreover,the results of O-O stretching vibrational frequency indicate that the K2O2 complexes is a redox state between the peroxo and superoxo.In the last chapter,a brief summary and vision is carried out.