Theoretical Investigations On The Structures And Properties Of Two-Dimensional Actinide Materials

Two-dimensional（2D）materials possess diverse applications across physics,chemistry,and materials science,making it crucial to develop innovative methods for designing,predicting,and synthesizing such materials.As theoretical calculation prediction tools advance,numerous 2D materials composed of s,p,and d-block elements have been predicted to stably exist,with some already successfully synthesized experimentally.However,research on 2D materials containing f-block elements remains scarce.Uranium,a common actinide f-block element in nature,plays a vital role in the nuclear industry,energy production,and military applications.Uranyl(UO₂²⁺)is a prevalent uranium-containing compound.Uranyl-based structural units can form clusters,as well as 2D and 3D materials in various dimensions.Studies indicate that some uranyl clusters exhibit topological structures akin to carbon clusters.Drawing on the topological structure similarities between uranyl and carbon clusters,we propose the potential existence of graphene-like 2D uranyl materials.Our research reveals that the uranyl and coordinated hydroxyl（U-（OH）₂-U）structures in uranyl clusters contribute to the formation of planar uranyl materials.We subsequently predicted a graphene-like 2D uranyl material with a hexagonal honeycomb structure through a global minimum search.Further investigation shows that the coordinated peroxy groups in 2D uranyl materials are superoxide O₂^-,and the singly occupied 2p_π*electrons form a one-dimensional antiferromagnetic Heisenberg chain.Additionally,the band structure calculations indicate that it is a semiconductor with a 3.4 e V bandgap.Phonon spectra and ab initio molecular dynamics（AIMD）calculations suggest that this 2D uranyl material exhibits good kinetic and thermodynamic stability,making it a promising candidate for further experimental synthesis.Recent studies have shown that fullerene clusters can aggregate to form 2D fullerene materials.Through theoretical calculations,we confirmed that the formation of C₆₀intermolecular bonds in this material stabilizes the 2D fullerene structure by transferring the internal carbon cage p electrons from p_πorbital of the isolated C₆₀ molecule to the p_σbonding orbital.Furthermore,we identified superatomic molecular orbitals with s,p,and d-orbital characteristics above its Fermi level,along with their resulting nearly-free electron bands.Building on this 2D fullerene,we designed 2D actinide-based endohedral metallofullerenes materials.We discovered that upon embedding U₂ molecules,the stability of the 2D fullerene significantly increases.Phonon spectra and AIMD simulation results also reveal good kinetic stability for these two materials.We then examined the multiple bonds between U-U and Th-Th in the actinide-embedded 2D fullerene structure.Our findings show that,due to the transfer between actinide dimers and carbon cages,five single-electron bonds form in the embedded U₂ 2D fullerene,while two single-electron bonds form in the embedded Th₂ 2D fullerene.