Structural Evolution and Electronic Properties of Two Sulfur Atom-Doped Boron Clusters

We present a theoretical study of structural evolution,electronicproperties, and photoelectron spectra of two sulfur atom-doped boronclusters S2B (n) (0/-) (n = 2-13), which reveal that the globalminima of the S2B (n) (0/-) (n = 2-13) clusters show an evolution froma linear-chain structure to a planar or quasi-planar structure. SomeS-doped boron clusters have the skeleton of corresponding pure boronclusters; however, the addition of two sulfur atoms modified and improvedsome of the pure boron cluster structures. Boron is electron-deficientand boron clusters do not form linear chains. Here, two sulfur atomdoping can adjust the pure boron clusters to a linear-chain structure(S2B2 (0/-), S2B3 (0/-), and S2B4 (-)), a quasi-linear-chain structure (S2B6 (-)), single- and double-chain structures(S2B6 and S2B9 (-)), and double-chain structures (S2B5, and S2B9). In particular, the smallest linear-chain boronclusters S2B2 (0/-) are shownwith an S atom attached to each end of B-2. The S2B2 cluster possesses the largest highest occupied molecularorbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gapof 5.57 eV and the S2B2 (-) clusterpossesses the largest average binding energy E (b) of 5.63 eV, which shows the superior chemical stability andrelative stability, respectively. Interestingly, two S-atom dopingcan adjust the quasi-planar pure boron clusters (B-7 (-), B-10 (-), and B-12 (0/-)) to a perfect planar structure. AdNDP bondinganalyses reveal that linear S2B3 and planarSeB(11) (-) have & pi; aromaticity and & sigma;antiaromaticity; however, S2B2, planar S2B6, and planar S2B7 (-) clusters have & pi; antiaromaticity and & sigma; aromaticity. Furthermore,AdNDP bonding analyses reveal that planar S2B4, S2B10, and S2B12 clustersare doubly (& pi; and & sigma;) aromatic, whereas S2B5 (-), S2B8, S2B9 (-), and S2B13 (-) clusters are doubly (& pi; and & sigma;) antiaromatic.The electron localization function (ELF) analysis shows that S2B (n) (0/-) (n = 2-13) clusters have different electron delocalizationcharacteristics, and the spin density analysis shows that the open-shellclusters have different characteristics of electron spin distribution.The calculated photoelectron spectra indicate that S2B (n) (-) (n = 2-13)have different characteristic peaks that can be compared with futureexperimental values and provide a theoretical basis for the identificationand confirmation of these doped boron clusters. Our work enrichesthe new database of geometrical structures of doped boron clusters,provides new examples of aromaticity for doped boron clusters, andis promising to offer new ideas for nanomaterials and nanodevices.