We have carried out first-principles calculations to explore the energetics and dynamics of Li in graphyne, a novel carbon allotrope consisting of spÀsp 2 hybridized carbon atoms, relevant for anode lithium intercalation in rechargeable Li-ion batteries. In contrast to graphite where Li diffusion is confined in the interlayer space (in-plane diffusion), the unique atomic arrangement and electronic structures enable both inplane and out-plane diffusion of Li ions in graphyne with moderate barriers, 0.53À0.57 eV. The highest Li intercalation density in graphyne can be LiC 4 , exceeding the up limit of LiC 6 in the commonly used graphite. The high lithium mobility and high storage capacity make graphyne a promising candidate for the anode material in battery applications.

Graphdiyne, consisting of sp- and sp(2)-hybridized carbon atoms, is a new member of carbon allotropes which has a natural band gap ~1.0 eV. Here, we report our first-principles calculations on the stable configurations and electronic structures of graphdiyne doped with boron-nitrogen (BN) units. We show that BN unit prefers to replace the sp-hybridized carbon atoms in the chain at a low doping rate, forming linear BN atomic chains between carbon hexagons. At a high doping rate, BN units replace first the carbon atoms in the hexagons and then those in the chains. A comparison study indicates that these substitution reactions may be easier to occur than those on graphene which composes purely of sp(2)-hybridized carbon atoms. With the increase of BN component, the band gap increases first gradually and then abruptly, corresponding to the transition between the two substitution motifs. The direct-band gap feature is intact in these BN-doped graphdiyne regardless the doping rate. A simple tight-binding model is proposed to interpret the origin of the band gap opening behaviors. Such wide-range band gap modification in graphdiyne may find applications in nanoscaled electronic devices and solar cells.

We carried out first-principles calculations to explore the oxidative longitudinal unzipping of single-walled carbon nanotubes (SWCNTs) of different diameters and chiralities. We found that the initial attack leading to nanotube unzipping prefers to occur in the middle region for armchair tubes, and at the tube ends for zigzag tubes. Once the initial attack has taken place, by overcoming an energy barrier whose value decreases with increasing tube diameter, the subsequent breakage of C-C bonds parallel to the ones broken in the former process is barrierless. The energetically preferred unzipping path is parallel to the tube axis for armchair tubes, resulting in straight zigzag-edged graphene nanoribbons. For zigzag tubes, there are two energetically equivalent unzipping directions corresponding to the opening of two types of C-C bonds tilted towards the tube axis, giving rise to helical unzipping paths. This is disadvantageous for the production of straight graphene ribbons. A local curvature modulation procedure is proposed to efficiently control the location of the initial attack and thus the shape of the produced graphene nanoribbons.

Discovering highly stable metal fullerenes such as the celebrated C 60 is interesting in cluster science as they have potential applications as building blocks in new nanostructures. We here investigated the structural and electronic properties of the fullerenes M 12 @Au 20 (M =Na, Al, Ag, Sc, Y, La, Lu, and Au), using a first-principles investigation with the density functional theory. It is found that these compound clusters possess a similar cage structure to the icosahedral Au 32 fullerene. La 12 @Au 20 is found to be particularly stable among these clusters. The binding energy of La 12 @Au 20 is 3.43 eV per atom, 1.05 eV larger than that in Au 32 . The highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap of La 12 @Au 20 is only 0.31 eV, suggesting that it should be relatively chemically reactive.

The conversion of normal prion protein (PrPC) into scrapie isoform (PrPSc) is a key event in the pathogenesis of prion diseases. However, the conversion mechanism has given rise to much controversy. For instance, there is much debate on the behavior of helix 1 (H1) in the conversion. A series of experiments demonstrated that H1 in isolated state was very stable under a variety of conditions. But, other experiments indicated that helices 2 and 3 rather than H1 were retained in PrPSc. In this paper, molecular dynamics (MD) simulation is employed to investigate the dynamic behavior of H1. It is revealed that although the helix 1 of Human PrPC (HuPrPC) is very stable in the isolated state, it becomes unstable when incorporated into native HuPrPC, which likely results from the long-range electrostatic interaction between Asp147 and Arg208 located in the helices 1 and 3, respectively. This explanation is supported by experimental evaluation and MD simulation on D147N mutant of HuPrPC that the mutant becomes a little more stable than the wild type HuPrPC. This finding not only help to reconcile the existing debate on the role of helix 1 in the PrPC-->PrPSc transition, but also reveals a possible mechanism for triggering the PrPC-->PrPSc conversion.