A theoretical study of electronic and vibrational properties of neutral, cationic, and anionic B24 clusters

The equilibrium geometries, electronic and vibrational properties, and static polarizability of B-24, B-24(-), and B-24(+) clusters are reported here. First-principles calculations based on density functional theory predict the staggered double-ring configuration to be the ground state for B-24, B-24(-), and B-24(+), in contrast to the quasi-planar structure observed in small neutral and ionized B-n clusters with n <= 15. Furthermore, the (4 X B-6) tubular structure is found to be relatively stable in comparison to the 3D cage structure. The presence of delocalized pi and multicentered sigma bonds appears to be the cause of the stability of the double-ring and tubular isomers. For the ground state of B-24, the lower and upper bound of the electron affinity is 2.67 and 2.81 eV, respectively, and the vertical ionization potential is 6.88 eV. Analysis of the frequency spectrum of the double-ring and tubular isomers reveals the characteristic vibrational modes typically observed in carbon nanotubes. The corresponding IR spectrum also reflects the presence of some of these characteristic modes in the neutral and ionized B-24, suggesting that double-ring and tubular structures can be considered as the building blocks of boron nanotubes. (C) 2005 Wiley Periodicals, Inc.