Rigorous Theoretical Investigation On The Ground State Configurations Of The Few-Layer Iodinene

Since the 1990s,nanomaterials have been included as a branch of materials science,and their development has been growing rapidly.Based on the spatial expression characteristics of nanomaterials,they can be divided into zero-dimensional,one-dimensional,two-dimensional,and three-dimensional,each with its unique properties.Researchers have designed materials with different dimensions,often resulting in new materials with novel properties for various application fields.Iodine is the only solid halogen element in the ocean that has non-toxic properties and good abundance.Due to its high concentration in the ocean,low extraction cost,good biocompatibility,and excellent theoretical electrochemical storage performance,iodine has broad applications in chemical analysis,medical,and new energy fields.In the field of new energy,iodine plays an important role in charge transfer in devices such as rechargeable alkaline metal ion batteries,dye-sensitized solar cells（DSSC）,and perovskite solar cells（PSC）.The crystal structure of solid iodine under environmental conditions is a three-dimensional layered molecular crystal composed of I₂.In 2020,researchers successfully prepared the few-layer structure of solid iodine through liquid-phase exfoliation and named it iodinene.They applied it in sodium-ion batteries,improving the performance of iodine-based batteries and verifying that iodine can stably exist in a few-layer two-dimensional structure.However,the real configuration of few-layer iodine has not been determined experimentally,and the models used in relevant theoretical studies are also inconsistent.Lack of a reasonable and detailed answer to this scientific question has prompted us to conduct this study from a rigorous theoretical perspective.According to the previous benchmark study on the functionals for the ground state of the crystalline iodine and bromine,the popular traditional functionals and the most hybrid functionals cannot describe the correct ground state with the molecular I₂arrangement.Considering this conclusion,as the first stage of this work,in Chapter 3,we first verified the availability of commonly used software packages,basis sets,and functionals.Finally,we determined that using the LC-ωPBE+D3 functional in the CRYSTAL17 software package is the most appropriate choice for studying the iodine system,and electronic structure calculations use the 8%hybrid B3LYP functional.In the ab initio molecular dynamics（AIMD）simulation calculations,the density functional tight-binding（DFTB）method can save a lot of computing resources,so we used the DFTB+software package based on the DFTB method for calculations.In Chapter 4,we discussed in detail the structure and stability of the few-layer iodine system and analyzed their maximum temperature of existence.According to our simulations,the few-layer iodine system can exist in the form of I₂molecules.In addition,Chapter 5 also discusses the van der Waals heterostructure system composed of single-layer iodine（1L-I₂）,single-layer graphene（G-I₂）,and sandwich form（G-I₂-G）.We found that the sandwich form of the G-I₂-G van der Waals heterostructure system enhances the thermodynamic stability of the single-layer iodine structure.We believe that this study can provide a clear answer to the above scientific questions and play a positive role in further related research.