Theoretical Study On Intra- And Intermolecular Interactions Of Superatoms

The concept of superatoms brings a new stage in the physical development of clusters.Superatoms can not only exhibit electronic structure properties similar to atoms,but also may exhibit more abundant physicochemical properties.The"bottom-up"composition structure of superatomic clusters can break the functional limitations when atoms are used as units to form materials,thus achieving high performance or even revolutionary applications.To achieve this,we need to have a deeper understanding of the intra-and inter-superatomic interactions,as well as to explain the physical mechanisms of superatomic interactions at the atomic level.In this thesis,based on the first principles method of quantum mechanics,we systematically study the structural characteristics of the superatomic system,forming a regular understanding of the intra-and inter-molecular mechanisms of superatoms.We propose a novel way to construct high angular momentum superatoms with light elements and find that the electron spin polarization can have an important influence on the inter-superatomic interaction.Then,we propose a new method to realize superatomic self-assembly based on the new dimension of electron spin polarization,and further discover the characteristics of electron transport changes related to the number of atomic numbers and units.Firstly,we investigate the mechanism of intra-superatomic interaction and find that the superatomic structure composed of light elements is promising to exhibit the characteristics of high angular momentum elements.There are great potentials in heavy elementsl for application because they contain high angular momentum electrons,however,these elements are generally rare and difficult to control on earth.Compared with heavy elements,there are advantages of low cost and low risk in light elements.In this part,a series of boron-nitrogen?BN?cages B_nN_n?n=12,16 and 28?have been studied and it is found that these structures all have superatomic properties.The superatomic electron configuration of B₁₂N₁₂ can be represented as1S²1P⁶1D¹⁰1F¹⁴2S²2P⁶1G¹⁸2D¹⁰1H¹⁰2F⁶,the superatomic electron configuration of B₁₆N₁₆6 and B₂₈N₂₈ can be represented as 1S²1P⁶1D¹⁰1F¹⁴1G¹⁸2S²2P⁶1H²²2D¹⁰2F¹⁴and1S²1P⁶1D¹⁰1F¹⁴1G¹⁸1H²²2S²2P⁶2D¹⁰2F¹⁴,respectively.More importantly,the electrons in these superatoms not only show S,P and D orbital symmetry similar to the low angular momentum electrons in atoms,but also generally show the F,G and even H orbital symmetry of higher angular momentum electrons.This discovery not only enriches the superatomic family,but also provides an important prospect for constructing new systems with light elements to show the electronic characteristics of high angular momentum.Secondly,we systematically investigate the inter-superatomic interactions.The interaction mechanism between superatoms is important both for understanding the novel molecular structure properties and for assembling properties based on superatoms.In this study,we form a series of superatomic interaction structures based on endohedral fullerenes?EMF?type superatomic An@C₂₈?An=Ac,Th,Pa and U?.Studies have shown that(U@C₂₈)₂ has demonstrated different chemical and physical adsorption states.Both adsorption comes from different magnetic coupling modes between U@C₂₈ superatoms,corresponding to the spin matching of one or two pairs of unpaired electrons,respectively.The robustness of the superatomic electronic structure is the key to form these two magnetic coupling modes.In the study of three inter-superatomic systems(Ac@C₂₈)(Pa@C₂₈),(Pa@C₂₈)₂ and(Th@C₂₈)₂,they demonstrate novel superatomic bonding properties.From the energy decomposition analysis,the specific gravity of each attraction determines that the three systems tend to be ionic,covalent and weakly interacting.Our study points out that these superatomic structures reproduce common bonding types in inter-atomic interactions and provide basic support for novel molecular systems formed with superatoms as units.Thirdly,based on the understanding of inter-superatomic interactions,we develop new controllable self-assembly methods.As an effective"bottom-up"method to construct functional materials and even devices,self-assembly has been a hot topic.Although impressive creativity and complex synthesis techniques have been demonstrated,difficulties remain in the precise control of self-assembled structures to fabricate functional materials.We constructed(U@C₂₈)_n assembly structures using EMF superatomic U@C₂₈ as units to develop a novel self-assembly method.In this method,the assembled units form a linear chain-like structure by magnetic coupling,and their own unpaired polarized electrons undergo spin matching,which ensures that the morphology of the components extends only along one-dimensional directions.Furthermore,theoretical calculations confirm that,in the absence of ligand passivation,EMF superatoms can effectively maintain their electronic structure in self-assembly due to the core-shell structure and regular electron arrangement,which ensures the self-assembly feasibility with superatoms as the basis.These findings highlight the electron spin polarization magnetic effect and can be an important driving source to achieve high precision self-assembly at the atomic level.Finally,as a further step based on previous studies,we have studied the electron transport properties of a series of superatoms as well as the assembled systems,demonstrating that the superatoms have the prospect of forming functionalized devices.In systems that contain both p and f electrons,the unique electronic structure produced by the hybrid of the two electrons may have potential applications in the design of molecular devices,spin devices,etc.Therefore,using the non-equilibrium Green function combined with the DFT method,we have carried out the study on the electron transport characteristics of EMF superatomic system.On the one hand,the research work shows that the electron transport capability of the EMF superatoms of An@C₂₈?An=Ac?Th?Pa and U?shows a trend of increasing with the increase of atomic number.The trend of their conductance values is Ac@C₂₈<Th@C₂₈<Pa@C₂₈<U@C₂₈,this is due to the increasing influence of strong electronic association effect of 5f electron orbit on the valence-layer electronic structure.On the other hand,the study also shows that as the number of assembled units increases from 2 to 5,the conductance value decreases by order of magnitude 10^-1 G₀ to 10^-8 G₀.These findings can be used to control the electrical conductivity by the number of assembled elements,that is,the length of chain structure,thus providing reference for the design of atomic level devices.In summary,the systematic work of this doctoral thesis will provide a reference for understanding the interaction in the superatomic system and play a positive role in the up-regulation of the structural and functional properties of the superatomic at the atomic level.