Geometrical Stability and Nonlinear Optical Properties of Crystallogen and Pnictogen Fullerene Analogues.

The linear and nonlinear optical (NLO) properties of fullerene and fullerene-like structures, including crystallogen and pnictogen elements, are computed quantum mechanically. The tensors of optical polarizability, α, and second hyperpolarizability, γ, for a series of buckyball fullerene analogues, namely, Si 60 , Ge 60 , Sn 60 , Pb 60 , P 60 , As 60 , Sb 60 , and Bi 60 , are reported and analyzed. The eight considered nanocages are here classified into four categories: nanocages stabilized in the X 60 form, including C 60 , As 60 , Sb 60 , and Bi 60 ; nanocages that are not stabilized in the X 60 form but are found to be stable in a distorted buckled b-X 60 form, with X = Si and Ge; nanocages stabilized only in an exohedral decorated X 60 -Y 60 form, X = Sn, Y = H or F; and finally nanocages that are not stable in either distorted or decorated form; however, their corresponding tabular nanotubes are found to be stable; such group includes P and Pb elements. A suggested nomenclature for the above-mentioned fullerenes is given for the first time, where many geometrical, energetic, and optical parameters are discussed extensively. These systems are energetically stable. The cohesive energies of Bi 60 and Sn 60 -F 60 range from -1.2 to -4.8 eV/atom and can be compared to -2.4 and -3.3 eV/atom from the corresponding 2D bismuthene and stanene monolayers, respectively. While bismuthellene, Bi 60 , shows vigorous optical responses compared to standard fullerene, the (9, 0) phosphorus nanotube gives not only enhanced polarizability and second hyperpolarizability but also an inducing first hyperpolarizability, β, which was null by symmetry in the case of spherical fullerenes. The proposed models are expected to be promising materials for optoelectronic and NLO applications.