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The stability, geometric structure and electronic properties of a novel body-centered tetragonal carbon allotrope Bct C 8 are systematically investigated. Bct C 8 are formed by sp 3 -bonded carbon atoms and can be regarded as a compressed bundle of carbon nanotubes (CNT). The transition path from CNT to Bct C 8 has been simulated, indicating a possible approach to synthesize Bct C 8 . The X-Ray diffraction, phonon and Raman spectroscopies are presented as reference for experimental studies. Besides, Bct C 8 is a semiconductor with an indirect gap of 1.66 eV and will transform to semimetal when doping with boron and nitride atoms. Furthermore, considering its porous structural character, the lithium storage capability of Bct C 8 are also discussed, a directional fast lithium-ion mobility with a rather low 0.04 eV barrier is revealed. Therefore, the Bct C 8 , once synthesized experimentally, would have fruitful applications in carbon-based electronics and energy storage. [ABSTRACT FROM AUTHOR]

The properties of diamond polytypes under high pressure have been investigated by means of the first-principles calculations. They are unveiled to be thermodynamically and kinetically more stable than hexagonal diamond (h-diamond) even under pressure. The electronic and elastic properties of the diamond polytypes are also explored, revealing very close cohesive energy, band gap and equilibrium density to those of cubic diamond (c-diamond). The Vickers hardness is uncovered to be comparable or even larger than those of the c- and h-diamond. Furthermore, they experience lower energy barriers than the h-diamond during the transforming process from graphite under pressure. Especially, we explored the characterized Raman modes under pressure from 0 to 40 GPa for each allotrope, which can be used to identify the diamond polytypes from the c-diamond T 2 g background mode, and the result may serve as a useful guide for future experimental studies. In addition, the simulated X-ray diffraction spectra under pressure is also presented. [ABSTRACT FROM AUTHOR]

A novel carbon allotrope, T-carbon, is attempted to obtain by using plasma enhanced chemical vapor deposition (PECVD) on the substrates of polycrystalline diamond and single crystalline diamond, respectively. Our measured x-ray diffraction, Raman and infrared spectra of the new form of carbon are in good agreement with the calculated results of T-carbon, and the lattice parameter meets with the results of calculation as well as the high resolution electron microscopy of T-carbon nanowires synthesized by the pulsed laser irradiating modification of carbon multiwall nanotubes, revealing that the phase of T-carbon can be identified in our samples. The experimental preparation of T-carbon by PECVD method indicates that the massive production of T-carbon may be feasible, and extensive investigations with high-throughput experiments on this novel phase are highly expected. Image 1 [ABSTRACT FROM AUTHOR]

Abstract: The geometric, electronic, and magnetic properties of twisted zigzag-edged graphene nanoribbons (ZGNRs) and novel graphene Möbius strips (GMS) are systematically investigated with the first-principles calculations based on the density functional theory. All the structures of ZGNRs and GMS are optimized, and their structural stabilities are examined. The molecular energy levels and the spin polarized density of states of ZGNRs are also calculated. It is found that the atomic bonding energies of the twisted ZGNRs decrease quadratically with the increase of the twisted angle, and the gaps between the lowest unoccupied molecular orbital and the highest occupied molecular orbital are varied with the twisted angle. The spin densities of ZGNRs and GMS reveal that the ground states with antiferromagnetic edges persist during the twisting, and the spin flip at some positions of the zigzag edges of GMS can be observed. [Copyright &y& Elsevier]