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Carbon-boron-nitride heteronanotubes have attracted much interest owing to their adjustable properties and wide applications in many fields. In this work, the structures and first hyperpolarizabilities ( β0) of a series of HA- n and isoelectronic PA- n heteronanotubes are investigated, in which HA- n is composed of a helical C segment and BN segment, and PA- n is composed of an arc C segment and BN segment. Interestingly, the helix C segment in HA-9 leads to a fascinating long-range charge-transfer character. As a result, the β0 value of HA-9 is 1.80×104 a.u., which is much larger than that of PA-9 (4.99×103 a.u.). Significantly, the β0 value of the C segment in HA-9 is 1.72×104 a.u., whereas that of the BN segment in HA-9 is much smaller (7.48×102 a.u.). In this context, the larger β0 value of HA-9 is essentially induced by the helix topological effect of the C segment. It is our expectation that this new knowledge about heteronanotubes might provide more ideas for further exploration of sp2-hybridized carbon segments with special topologies. [ABSTRACT FROM AUTHOR]

The unusual properties of species with excess electrons have attracted a lot of interest in recent years due to their wide applications in many promising fields. In this work, we find that the excess electron could be effectively bound by the B atoms of boron nitride nanotube (BNNT), which is inverted pyramidally distributed from B-rich edge to N-rich edge. Further, Li@ B-BNNT and Li@ N-BNNT are designed by doping the Li atom to the two edges of BNNT, respectively. Because of the interaction between the Li atom and BNNT, the 2s valence electron of Li becomes a loosely bound excess electron. Interestingly, the distribution of the excess electron in Li@ N-BNNT is more diffuse and pyramidal from B-rich edge to N-rich edge, which is fascinating compared with Li@ B-BNNT. Correspondingly, the transition energy of Li@ N-BNNT is 0.99 eV, which is obviously smaller than 2.65 eV of Li@ B-BNNT. As a result, the first hyperpolarizability (3.40×104 a.u.) of Li@ N-BNNT is dramatically larger (25 times) than 1.35×103 a.u. of Li@ B-BNNT. Significantly, we find that the pyramidal distribution of the excess electron is the key factor to determine the first hyperpolarizability, which reveals useful information for scientists to develop new electro-optic applications of BNNTs. [ABSTRACT FROM AUTHOR]