Theoretical Studies On The Electronic Structures Of High Angular Momentum Superatomic Systems

In molecular systems,f electrons with high angular momentum could be symmetrically coupled with any kinds of s,p,d,f orbital in principle,and then a hybridization occur.Although the characters of light lanthanide and actinide elements are not dominant by f electrons completely,they still are called f-block elements because that 4f and 5f electrons which are valence shell electrons play a key role in bonding and interaction between these elements and other molecules or atoms.They not only possess several unfilled subshells,they also could present extremely complicated electronic state structure in the whole molecule system when they are influenced by limited range.As an important outer covering limited range in superatom,with the hybridization between d and s valance orbitals and relativistic effect,shell structure unveil the potential application value of coinage metal nanoparticles in photology,electricity,magnetism and biomedicine,etc.Therefore,the research on optical properties of bimetallic nanoparticles has become a hotspot issues.On the other hand,the spectroscopic properties of actinide also play a remarkable role in the regular arrays of metals.Because the absorption and/or emission lines of 5f valence shell electrons are narrow and sharp in the visible range,and these spectra lines could be also hardly influenced by external coordination environment.Consequently,the superatom models comprised of f–block and ds–block elements could be envisioned,very likely carrying a revolutionary spectroscopic performance.Surface-enhanced Raman scattering?SERS?is a powerful spectroscopy technique for highly sensitive molecular detection.5f-elements encaged in gold superatomic cluster are capable of giving rise to unique optical properties due to their hyperactive valence electrons and great radial extent of 5f/6d orbitals.Herein,we review our first-principles studies on electronic structures and spectroscopic properties of a series of actinide-embedded gold superatomic clusters with different dimensions.The three-dimensional and two-dimensional superatom clusters possess the 18-electron configuration of 1S²1P⁶1D¹⁰ and 10-electron configuration of 1S²1P⁴1D⁴,respectively.Importantly,their electronic absorption spectra can be also effectively interpreted by the superatom orbitals.Specifically,the charge transfer?CT?transitions involved in surface-enhance Raman spectroscopy?SERS?spectra for three-and two-dimensional structures are all from the filled 1D orbitals,providing the enhancement factors on the order of 104 at 488 nm and 105 at 456 nm,respectively.This work implies that,the superatomic orbital transitions involving in 5f-elements not only can lead to a remarkable spectroscopic performance,but also a new direction for optical design in future.It is well known that the coinage metal silver exhibits strong plasma absorption in the UV-vis region compared to gold,and it is possible to further adjust the selection interval of its excitation light.The 5f-element-containing clusters,An@Ag₁₄?An = Ac-,Th,Pa+?,can be viewed as superatomic systems(1S²1P⁶1D¹⁰).Taking them to be surface-enhanced Raman scattering?SERS?substrate,the charge-transfer states?1Dmetal ? ?*pyridine?can lead to SERS signal enhancement ¹04 for pyridine-Th@Ag₁₄ complexes,which is found to be superior to the pure silver systems.Furthermore,considering the damage of the sample,the operating cost,the interference of fluorescence as well as other factors,the > 600 nm?especially 633 nm?excitation light always offers a good compromise between high SERS intensities and the above-mentioned factors.As a result,actinide-encapsulated silver-cage superatom clusters serving as substrate materials are suitable for applications because their SERS peaks could resonate with the experimentally common 633 nm excitation lines.Therefore,this work is promising to provide a theoretical basis for the design and synthesis of actinide–silver alloy SERS substrate materials.Based on the research above,we found that the superatoms with f-block element as the core would always satisfy 18-electron rule preferentially,no matter it is gold-coated or silver-coated.However,as the atomic number of actinide increase,f electrons will be filled into 5f shell constantly.In order to reduce the energy,the adjustment to geometric construction will lead to the relaxation of 5f electrons and the reconstitution of bonding behavior.So that whether the electron counting rule is still applicable for actinide?An,for short?elements has aroused widespread concern.In our theoretical research on the structures of Au₁₄ with actinides?Th,Pa,U,Np,Pu?encapsulated in it,we found that they still satisfy the 18-electron rule.They correspond to superatom states 1S²1P⁶1D¹⁰1F⁰,1S²1P⁶1D¹⁰1F¹,1S²1P⁶1D¹⁰1F²,1S²1P⁶1D¹⁰1F³ and 1S²1P⁶1D¹⁰1F⁴,respectively.One thing need to be noticed is that,from Th to Pu atom,5f electrons perform the shift from valence orbital electrons to core orbital electrons.With further spin topological analysis,when Pa atom are embedded in the structure,5f atoms show more delocalization,which lead to the ferromagnetism Pa@Au₁₄ represent.When Np and Pu atoms are embedded,5f atoms would show more localization,which lead to the antiferromagnetism Np/Pu@Au₁₄ represents.However,the localization or delocalization of 5f electrons when Th and U are embedded is not very obvious.We hope that this research could provide some theoretical basis for the design and manufacture of molecules with high angular momentum.The electronic and energetic consequences in [H₂Ag₄₄?SR?₃₀]n-to form [2HAg₄₄?SR?₃₀]n-?where n = 2,4,6?were studied by density functional theory?DFT?methods.Among them,the six typical geometries with superatomic electronic configurations are [H₂Ag₄₄?SR?₃₀]2-?2e@16e?,[H₂Ag₄₄?SR?₃₀]4-?2e@18e?,[H₂Ag₄₄?SR?₃₀]6-?2e@20e?,and [2HAg₄₄?SR?₃₀]2-?18e?,[2HAg₄₄?SR?₃₀]4-?20e?,[2HAg₄₄?SR?₃₀]6-?22e?.It is obvious that [H₂Ag₄₄?SR?₃₀]4-is the most stable amongst the former series,because it retains a dihydrogen molecular with two electrons?? bonding?and an 18 e superatomic cluster(1S²1P⁶1D¹⁰).Similarly,[2HAg₄₄?SR?₃₀]2-absorbs the two electrons from the two dissociated H atoms to achieve the overall electron count of 18 is the most stable amongst the latter series.Besides,five continuous virtual reactions were identified.The endoic addition of H₂ to a metal cluster was found to be a reductive addition reaction,in sharp contrast to the well-studied oxidative addition of a H₂ molecule to a metal complex to form ?2-H₂ M complexes with a side-on dihydrogen.Furthermore,while the latter reactions are generally exothermic,the former are endothermic in nature owing to the spatial confinement.In consideration of the unique physicochemical properties of superatoms and its potential application value,to ascertain the interaction principles between superatoms has an important significance to apply them into practice.Taking Th@Au₁₄-Th@Au₁₄ dipolymer as an example,we provide a general interpreting about the stable combination of superatom clusters.In Chapter Four,we introduce that Th@Au₁₄ possess 1S²1P⁶1D¹⁰ superstom state.According to hypervalent bonding theory,the interaction between two 1S superatom orbitals lead to the formation of bonding orbital and * antibonding orbital.The interaction among six 1P superatom orbitals lead to the formation of three bonding orbitals and three * antibonding orbitals.And the interaction among ten superatom orbitals lead to the formation of five bonding orbitals and five * antibonding orbitals.Both the bonding orbitals and the antibonding orbitals,for the eight atoms on the joint point,are all bonding orbitals,which will benefit the structure stability.Therefore,Th@Au₁₄ superatoms dipolymer could be a perfect combination in geometric construction and electronic structure.With the deepening of the research,we expect that,on the premise of the stabilities of electronic and geometric structure,a more advanced package assembly will become reality.Profound understanding the interaction inner molecule and among different molecules will be decisive for the design and application of superatoms.In theoretical study,energy decomposition analysis?EDA?method is widely accepted as a quantum computing tool.However,for the elements with high angular momentum,the same electronic state with different electron occupying pattern will lead to totally different results,which need to be revised by adjusting the configuration of the atoms in molecular systems.We take the typical structures,Ac@Au7 and Th@Au₁₄ as examples,to speculate on the fragments of some atoms and molecules,and the comparison analysis found that the closed shell initial fragment we usually use is not quite reasonable.A more reasonable energy decomposition component needs to be obtained by estimate the electron occupying pattern of the fragments according to charge transformation and electron density analysis.Hence,through the correct electron partition,we can understand and analyze the interaction energy?bonding energy?of the elements with high angular momentum.