Narrow Results

Optimized geometries and vibrational frequencies of polydiacetylenes (PDAs) and their derivatives were studied by density functional calculations at the B3LYP/6-31G* level. The time-dependent density functional theory was used to determine their vertical transition energies and corresponding oscillator strengths. Calculations show that different side groups in these linear carbon chains can significantly modify their structural and electronic properties, whereas the effect of terminal substitution is negligible. Predicted equilibrium geometries indicate that the single, double, and triple bonds of PDAs and their derivatives are almost unchanged as the chain increases, showing a remarkable character of localized bond. The periodic boundary condition calculations reveal that the strongest adsorption for the infinite chain of PDA appears at 723 nm, and the HOMO → LUMO excitation is responsible for this strong electronic transition.

Geometries associated with relative stabilities and energy gaps of the Mo-doped boron clusters have been investigated systematically by using density functional theory. The critical size of Mo-encapsulated B_n structures emerges as n = 10, the evaluated relative stabilities in term of the calculated fragmentation energies reveal that the MoB₆ has enhanced stabilities over their neighboring clusters. Furthermore, the calculated polarities of the MoB_n reveal that the hypercoordinated planar MoB₁₀ wheel is a weakened polar molecule and MoB₁₁ ring is a nonpolar molecule, and aromatic properties are discussed. Additionally, the MoB₁₀ cluster with smaller highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap is supposed to be stronger chemical activity and smaller chemical hardness. Moreover, the recorded natural populations show that the charges transfer from boron framework to Mo atom. It should be pointed out that the remarkable charge-transfer features of MoB_n clusters are distinctly similar to those of transitional metal (TM)-doped Si_n clusters; growth-pattern of the TMB_n depends on the doped TM impurity.