Structural Stabilities and Electronic Properties Jan 20, 2014 Stability 374 There is a striking evolution of boron nanostructures[1] with the increasing size confirmed by experimentalists and theorists, due to the electron deficiency. Computational prediction of B80[2] suggests that a triangular boron lattice with proper vacancies should be more stable, leading to extensive searches of possible planar sheets[3,4] and nanotubes[4] with various concentration and distribution of vacancies. The boron sheet is metal, and there are bands similar to the pi bands in the graphene near the Fermi level. Rolled from the sheet, the nanotubes with diameter larger than 17 Å are metals. Smaller nanotubes are semiconductors with the gap decreasing as the diameter and chiral angle increase. Experimental observations[5,6] showed that stable boron clusters were planar triangular fragments with tetragonal, pentagonal, and hexagonal vacancies. In our recent work[7],we have performed High-Throughput screening for possible B clusters through the first-principles calculations. Combined with a congruence check, we have determined the structures of Bn clusters with n=30~51, and found a stable planar cluster of B49 with a double-hexagon vacancy. We have also proposed an effective model for describing the two-center two-electron (2c-2e) and three-center two-electron (3c-2e) bonds’ distribution, which is in agreement with the charge difference satisfying the geometry’s symmetry. Our model is found to be universal for the high stabilities of planar clusters (B36 and B49+) and recently observed cages (B40)[6]. B36 with hexagonal vacancies can be considered the precursor of borophene, where the nomenclature of borophene was initially proposed [5] and refers to a graphene‐like B sheet with vacancies. The recent experiment[8] reported that the borophene formed on the Ag (111) surface was a buckled triangular lattice without vacancy. In our work[9], we have proposed a novel nucleation mechanism of boron clusters and demonstrated a clear picture of borophene’s growth: (1) small boron clusters deposited on the silver surface would expel Ag atoms on top to form Ag vacancies, where hexagonal vacancies are necessary as the cluster size increases; (2) boron clusters with the zigzag edge are stabilized due to the strong B-Ag interaction and the ones with the vacancies in a stripe pattern are most stable. #### References [1] H. J. Zhai, B. Kiran, J. Li, and L. S. Wang, Nat. Mater. 2, 827 (2003). [2] N. G. Szwacki, A. Sadrzadeh, and B. Yakobson, Phys. Rev. Lett. 98, 166804 (2007). [3] H. Tang, S. Ismail-Beigi,Phys. Rev. Lett. 99, 115501(2007). 142, 214307(2015). [4] X. B. Yang, Y. Ding, and J. Ni, Phys. Rev. B 77, 041402 (2008). [5] Z. A. Piazza, H. S. Hu, W. L. Li, Y. F. Zhao, J. Li, and L. S. Wang, Nat.Commun. 5, 3113 (2014). [6] H. J. Zhai et al., Nat. Chem. 6, 727 (2014). [7] S.G Xu Y. J. Zhao, J. H. Liao and X.B. Yang*, J. Chem. Phys. [8] A. Mannix et.al Science, 350,1513(2015) [9] S.G Xu and X.B. Yang* et. al, Nano Research,9, 2616 (2016)
