The reduced graphene oxide (RGO)-based composites have attracted intensive attention in experiment due to its superior performance as photocatalysts, but still lacking is the theoretical understanding on the interactions between constituents, and the connection between such interaction and the enhanced photoactivity. Herein, the interaction between the g-C 3 N 4 and RGO sheets is systematically explored by using state-of-the-art hybrid density functional theory. We demonstrate that the O atom plays a crucial role in the RGO-based composites. Compared to the isolated g-C 3 N 4 monolayer, the band gap of composites obviously decreases, and at higher concentration, the levels in the vicinity of Fermi level are much more dispersive, indicating the smaller effective mass of the carrier. These changes are nonlinear on the O concentration.Interestingly, appropriate O concentration alters the direct-gap composite to indirect-gap one.Most importantly, at a higher O concentration, a type-II, staggered, band alignment can be obtained in the g-C 3 N 4 -RGO interface, and negatively charged O atoms in the RGO are active sites, leading to the high hydrogen-evolution activity. Furthermore, the calculated absorption spectra varying with the O concentration shed light on different experimental results. The findings pave the way for developing RGO-based composites for photocatalytic applications.

The effect of the cooling rate on the solidification process of liquid aluminium is studied using a large-scale molecular dynamics method. It is found that there are various types of short-range order (SRO) structures in the liquid, among which the icosahedral (ICO)-like structures are dominant. These SRO structures are in dynamic fluctuation and transform each other. The effect of the cooling rate on the microstructure is very weak at high temperatures and in supercooled liquids, and it appears only below the liquid-solid transition temperature. Fast cooling rates favour the formation of amorphous structures with ICO-like features, while slow cooling rates favour the formation of FCC crystalline structures. Furthermore, FCC and HCP structures can coexist in crystalline structures. It is also found that nanocrystalline aluminium can be achieved at appropriate cooling rates, and its formation mechanism is thoroughly investigated by tracing the evolution of nanoclusters. The arrangement of FCC and HCP atoms in the nanograins displays various twinned structures as observed using visualization analysis, which is different from the layering or phase separation structures observed in the solidification of Lennard-Jones fluids and some metal liquids.

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We present a novel method to identify local structures in disordered systems according to topological criteria. Its effectiveness is demonstrated in the analysis of the atomic structures in the rapid cooling of silver liquid. The method is parameter free and scale independent, and can generally be used for structural analysis of amorphous systems involving atoms or particles at different length scales.

To deeply understand the formation mechanism of a critical nucleus during the nucleation process of liquid metal sodium, a system consisting of 10 000 Na atoms has been simulated by using molecular dynamics method. The evolutions of nuclei are traced directly, adopting the cluster-type index method. It is found that the energies of clusters and their geometrical constraints interplay to form the favorable microstructures during the nucleation process. The nucleus can be formed through many different pathways, and the critical size of the nucleus would be different for each pathway. It is also found that the critical nucleus is nonspherical and may include some metastable structures. Furthermore, the size of the cluster and its internal structure both play a crucial role in determining whether it is a critical nucleus, and this is in agreement with the simulations by computing the free energy of the Lennard-Jones system [D. Moroni, P. R. ten Wolde, and P. G. Bolhuis, Phys. Rev. Lett. 94, 235703 (2005)].

On the basis of the quantum Sutton-Chen potential, the rapid solidification processes of liquid silver have been studied by molecular dynamics simulation for four cooling rates. By means of several analysis methods, the competitions and transitions between microstructures during the cooling processes have been analyzed intensively. It is found that there are two phase transitions in all simulation processes. The first one is from liquid state to metastable (transitional) body-centered cubic (bcc) phase. The initial crystallization temperature T(ic) increases with the decrease of the cooling rate. The second one is from the transitional bcc phase to the final solid phase. This study validates the Ostwald's step rule and provides evidence for the prediction that the metastable bcc phase forms first from liquid. Further analyses reveal that the final solid at 273 K can be a mixture of hexagonal close-packed (hcp) and face-centered cubic (fcc) microstructures with various proportions of the two, and the slower the cooling rate is, the higher proportion the fcc structure occupies.

This study demonstrates the details on the twinned structure and growth process of V-shaped silver nanowires with different bending angles (e.g., 90°, 120°, and 135°) confirmed by high-resolution transmission electron microscopy (HRTEM). These nanowires could be synthesized by a facile but effective polyol−thermal reaction method in autoclaves (160−180 °C). The nearly uniform-size silver nanowires show an average diameter of ∼45 nm and length up to tens of micrometers. The microstructure and optical properties of the silver nanowires were characterized by various advanced techniques, including TEM, HRTEM, scanning electron microscopy (SEM), and ultraviolet−visible (UV−vis) spectroscopy. The twinned structure can occur in both silver spherical particles and nanowires, confirmed by HRTEM analysis and also simulated by molecular dynamics methods. The growth of V-shaped nanowires by two possible means was particularly investigated: (i) crystal lattice match-induced end-to-end or end-to-side fusion of two nanowires, and (ii) twinned crystal plane-induced growth. Such structural and mechanistic understanding of silver crystals would be useful for the shape, size, and property control of functional nanoparticles.

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