First-principles Calculation And Design Of Nonlinear Optical Materials Containing D¹⁰ Electron Configuration Cations

It is an effective way to predict new materials by exploring the influence mechanism of micro-groups on the macroscopic performance,to realize the effective design of nonlinear optical material.Introducing groups with asymmetric charge density are one of the effective methods to enhance the nonlinear optical response.The metal cations with d¹⁰ electron configuration containing polar shifts to combine with anionic groups to form a group with asymmetric charge density distribution,thus it is expected to produce a large nonlinear optical response.Therefore,the impact mechanism of d¹⁰ electron configuration metal cations on the microstructure in nonlinear optical crystal materials is explored.Then,we can further clarify the relationship between microstructure and macroscopic performance,and provide theoretical guidance for the design and prediction of nonlinear optical crystal materials with excellent performance.Based on density functional theory,this paper aims to study the influence mechanism of d¹⁰ metal cations with polar shifts in nonlinear optical crystal materials,and design new nonlinear optical crystal materials.The specific contents are as follows:（1）The mechanism of the electronic structure changes and the source of optical properties in MIn S2（M=Ag,Li）are systematically studied.The orbital hybridization,atomic size effect and cation electronegativity caused changes in bandgap and optical properties were revealed.By replacing the A-site cation,the electronic structure changes of the silver cations containing d¹⁰ electron configuration introduced into the framework of the In-S anion groups were analyzed.In these two compounds,except for the important contributions of In-S anion groups to the bandgap and nonlinear optical properties,we also found that the contributions of Ag cations with d¹⁰ electron configuration cannot be ignored.Besides,the electronic structures of the S atoms in MIn S2（M=Ag,Li）are susceptible to the type of cations at the A-site,which affects the nonlinear optical properties.（2）As one kind of promising deep-ultraviolet nonlinear optical crystal materials,fluorooxoborates have rich structural types,and excellent nonlinear optical properties and have different metal cation changes under the same anion group framework.Herein,the general mechanism of the metal cations effect on the bandgap and optical properties in a series of typical fluorooxoborates is elucidated.By analyzing the representative 18-membered ring fluorine-oxygen framework in different fluorooxoborates crystal structures,a new stable structure of Cd B5O7F3 was designed.The results show that the18-membered ring fluorine-oxygen framework has very excellent flexibility and can accommodate different cations from alkali metal elements to d¹⁰ metal elements.Also,the introduction of d¹⁰ electron configuration metal cations in the fluorine-oxygen anion frameworks can significantly enhance the nonlinear optical effect（3.1×KH2PO4,d36=0.39 pm/V）,and can also maintain the deep-ultraviolet transmission.Therefore,the fluorooxoborates containing d¹⁰ electron configuration metal cations have great potential to become new types of deep-ultraviolet nonlinear optical crystal materials.