Document Type : Research Article
Department of materials and Metallurgical Engineering, Technical and Vocational University (TVU), Tehran, Iran
In present computational survey, we are compared and contrasted electronic effects of C20 and its C20-2nTinBn heterofullerenic derivatives with n = 1-5, at density functional theory (DFT). All nanocages are true minima and none of them collapses to deformed open cage as segregated nanostructure. Isolating five single hetero bonds of Ti—B via either one double bond of C═C or one carbon atom is a suitable method for reaching highly substituted stable heterofullerene i.e. pen-shell C10Ti5B5 since it prevents from weak homo bonding of Ti—Ti and B—B. The C1-C18Ti1B1 heterofullerene can avoid from the most strained directly fused five-pentagon configuration, but its open-shell electronic structure with highly pyramidalized titanium atom (126.59° i.e. 3-4 times relation to C20) may render it too reactive to be observed under typical experimental conditions. The calculated binding energy (B.E.) shows C10Ti5B5 as the most stable heterofullerene. Contrary on B.E., the absolute heat of atomization of heterofullerenes decreases as number of substituting Ti―B unit (n) increases. Hence, substitution effect on binding energy is more significant than heat of atomization. Compared to the previously reported material such Ti-decorated B38 nanofullerene as a suitable hydrogen storage with B.E. of 5.67 eV/atom, our studied C20-2nTinBn heterofullerenes show the higher B.E. with range of 12.25 to 38.03 eV/atom, the higher stability and the higher capacity for hydrogen storage. Interestingly, C18Ti1B1 heterofullerene must be not only kinetically stable against electronic excitations but also based on natural bond orbital (NBO) analysis, the highest charge transfer (CT) is take placed from πC=C bonds to the neighboring LP*B, LP*Ti and σ*Ti-B anti-bonds of it. Also, the exceptionally large value of nucleus-independent chemical shifts (NICS) is found for C18Ti1B1 compared to the archetypically aromatic benzene and [2.2]paracyclophane molecules.