The competition of double-, four-, and three-ring tubular B(3n) (n = 8-32) nanoclusters.

The geometry and electronic properties of three-ring tubular B(3n) clusters (n = 8-32) are studied systematically with the density functional theory. It is composed of three staggered rings with the diameter of the middle ring larger than those of the two outer rings. With the increase in boron atom numbers, the three-ring tubular clusters are energetically more stable than the double-ring and four-ring tubular clusters and the buckled sheet clusters with hexagon holes. The average binding energy tends to the finite value. The stability is further analyzed through the natural bond orbital population analysis. The highest occupied and lowest unoccupied energy gaps become small, which demonstrates a favorable metallic property.