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Fullerene-based sandwiches have emerged as new candidates for potential applications of two-dimensional nanomaterials in electronics or energy storage. Recently, experimentalists have observed the evolution of boundaries for fullerene clusters sandwiched by two graphene layers, while vacuum space with typical dimension of 30 {\AA} was found within the fullerene layer. Because the pattern of the fullerene cluster impacts the physical properties of the sandwiches, it is important to understand the mechanisms for their structural transformations. In the present work, we find that the graphene/fullerene/graphene sandwich structure transforms among three configurations, depending on the fullerene to graphene area ratio. Molecular dynamics simulations show that there are two critical values for the area ratio. The fullerene pattern transforms from circular to rectangular at the first critical area ratio of 1/{\pi}. The critical value of 1/{\pi} is successfully derived by comparing the geometrical perimeter of the circular and rectangular shapes for the fullerene cluster without any physical parameters. At the second critical area ratio, the graphene layers surrounding the fullerene cluster become separated due to the competition between the bending energy and the cohesive energy. Based on the analytic model, the vacuum space is predicted to be 34 {\AA}, which agrees quite well with the experimental result. These findings provide fundamental insights into the mechanisms driving structural transformation of fullerene-based sandwiches, which will enable the selection of appropriate structures and materials to guide the design of future electronic and energy storage applications.

Zirconia is well-known for plenty of important morphologys with Zr coordination varying from sixfold in the octagonal phase to eightfold in the cubic or tetragonal phase. The development of empirical potentials to describe these zirconia morphologys is an important issue but a long-standing challenge, which becomes a bottleneck for the theoretical investigation of large zirconia structures. In contrast to the standard core-shell model, we develop a new potential for zirconia through the combination of long-range Coulomb interaction and bond order Tersoff model. The bond order characteristic of the Tersoff potential enables it to be well suited for the description of these zirconia morphologys with different coordination numbers. In particular, the complex monoclinic phase with two inequivalent oxygens, that is difficult to be described by most existing empirical potentials, can be well captured by this newly developed potential. It is shown that this potential can provide reasonable predictions for most static and dynamic properties of various zirconia morphologys. Besides its clear physical essence, this potential is at least one order faster than core-shell based potentials in the molecule dynamics simulation, as it discards the concept of the ultralight shell that demands for an extremely small time step. We also provide potential scripts for the widely used packages GULP and LAMMPS., Comment: Tersoff potential scripts for GULP and LAMMPS are available from www.jiangjinwu.org

We parametrize the Stillinger-Weber potential for 156 two-dimensional atomic crystals. Parameters for the Stillinger-Weber potential are obtained from the valence force field model following the analytic approach (Nanotechnology 26, 315706 (2015)), in which the valence force constants are determined by the phonon spectrum. The Stillinger-Weber potential is an efficient nonlinear interaction, and is applicable for numerical simulations of nonlinear physical or mechanical processes. The supplemental resources for all simulations in the present work are available online in Ref. 1, including a fortran code to generate crystals' structures, files for molecular dynamics simulations using LAMMPS, files for phonon calculations with the Stillinger-Weber potential using GULP, and files for phonon calculations with the valence force field model using GULP., Comment: 25 more crystals are included. All structure codes and simulation scripts (using LAMMPS and GULP) are available online at: http://jiangjinwu.org/sw

The single-layer black phosphorus is characteristic for its puckered configuration that possesses the hinge-like mechanism, which leads to the highly anisotropic in-plane Poisson's ratios and the negative out-of-plane Poisson's ratio. We reveal that the hinge-like mechanism can be attributed to the angle-angle cross interaction, which, combined with the bond stretching and angle bending interactions, is able to provide a good description of the mechanical properties in the single-layer black phosphorus. We also propose a nonlinear angle-angle cross interaction, which follows the form of the Stillinger-Weber potential and is advantageous for molecular dynamics simulations of single-layer black phosphorous under large deformations., Comment: GULP, LAMMPS

We derive an analytic formula for the Young's modulus in single-layer black phosphorus using the valence force field model. By analyzing the directional dependence for the Young's modulus, we explore the third principle direction with direction angle phi_tp = 0.268pi besides armchair and zigzag directions. The maximum Young's modulus value is in the third principle direction. More specifically, the Young's modulus is 52.2 N/m, 85.4 N/m, and 111.4 N/m in the armchair direction, zigzag direction, and the third principle direction, respectively. This new principle direction is of significance for future discussions of other anisotropic properties in the single-layer black phosphorus., Comment: 5 pages, 3 figs. arXiv admin note: text overlap with arXiv:1410.3545

Reactions of monoanions {M(CO) 3 [η 5 -C 5 H 4 C(O)CH 2 CH 2 CO 2 Me]} − with RuCo 2 (CO) 9 (μ 3 -Se) in THF at 60°C gave two new cluster derivatives (μ 3 -Se)CoMRu(CO) 8 [η 5 -C 5 H 4 C(O)CH 2 CH 2 CO 2 Me] (M=Mo 1 , M=W 2 ). Similarly, reactions of dianions − {M(CO) 3 [(η 5 -C 5 H 4 )C(O)CH 2 CH 2 C(O)(η 5 -C 5 H 4 )](CO) 3 M} − with two molecules of RuCo 2 (CO) 9 (μ 3 -Se) gave 1,4-succinoyl(biscyclopentadienyl)-bridged double cluster complexes (μ 3 -Se)CoMRu(CO) 8 [(η 5 -C 5 H 4 )C(O)CH 2 CH 2 C(O)(η 5 -C 5 H 4 )]CoMRu(CO) 8 (μ 3 -Se) (M=Mo 3 , M=W 4 ). Treatment of cluster (μ 3 -Se)CoMoRu(CO) 8 [(η 5 -C 5 H 4 )C(O)Me] with ammine derivatives 2,4-dinitrophenylhydrazine, NH 2 NHC(S)NH 2 , (−)-5-(α-phenyl)semioxamazide and l -(+)-menthydrazide, respectively, at room temperature produced four new hydrazone cluster derivatives (μ 3 -Se)CoMoRu(CO) 8 [η 5 -C 5 H 4 C(NR)Me] (R=NHC 6 H 3 -2,4-(NO 2 ) 2 5 , R=NHC(S)NH 2 6 , R=NHC(O)C(O)NHCH(Me)(C 6 H 5 ) 7 , R=NHCO 2 -menthyl 8 ). However, cluster 1 can only react with 2,4-dinitrophenylhydrazine to give the formation of cluster (μ 3 -Se)CoMoRu(CO) 8 [η 5 -C 5 H 4 C(NR)CH 2 CH 2 CO 2 Me] (R=NHC 6 H 3 -2,4-(NO 2 ) 2 9 ) under similar condition. Although, two kinds of optically active groups have been introduced into cluster (μ 3 -Se)CoMoRu(CO) 8 [(η 5 -C 5 H 4 )C(O)Me], the mixture of diastereoisomers could not be separated by silica gel chromatography. The 13 C-NMR spectra showed the presence of a pair of diastereoisomers.

The reactions of dipropargyl manolate and terephthalate, respectively, with Co2(CO)8 in THF at room temperature gave four new compounds [R(CO2CH2C2H-μ)2][Co2(CO)6]2 (R=CH2, 1a; R=C6H4, 1b) and [(HC2CH2OCO)R(CO2CH2C2H-μ)][Co2(CO)6] (R=CH2, 2a; R=C6H4-1,4-, 2b), and compounds 2a and b reacted with RuCo2(CO)11 to form two new linked clusters [R(CO2CH2C2H-μ)2][Co2(CO)6][RuCo2(CO)9] (R=CH2, 3a; R=C6H4-1,4-, 3b). The treatment of two dipropargyl esters, respectively, with RuCo2(CO)11 afforded another two new clusters [R(CO2CH2C2H-μ)2][RuCo2(CO)9]2 (R=CH2, 4a; R=C6H4-1,4-, 4b). The reactions of dipropargyl manolate, terephalate with Mo2Cp2(CO)4 gave rise to the formation of dinuclear complexes [(HC2CH2OCO)R(CO2CH2C2H-μ)][Mo2Cp2(CO)4] (R=CH2, 5a; R=C6H4-1,4-, 5b), compound 5a reacted with Co2(CO)8 to produce the cluster [CH2(CO2CH2C2H-μ)2][Co2(CO)6][Mo2Cp2(CO)4] 6a. All the new clusters have been characterized by C/H elemental analysis, IR and 1H NMR spectroscopies. The structure of [CH2(CO2CH2C2H-μ)2][Co2(CO)6]2 1a and [p-(HC2CH2OCO)C6H4(CO2CH2C2H-μ)][Co2(CO)6] 2b have been determined by single crystal X-ray diffraction methods.

The phonon modes at finite temperature in graphene and single-walled carbon nanotubes (SWCNT) are investigated by the mode projection technique combined with molecular dynamics simulation. It is found that the quadratic phonon spectrum of the flexural mode in graphene is renormalized into linear at finite temperature by the phonon-phonon scattering. Possible influence of this renormalization on the electron-phonon interaction and phonon thermal transport is analyzed. For the SWCNT, however the quadratic property of the phonon spectrum for the flexural mode can survive at finite temperature under protection of the two-fold degeneracy of the flexural mode in SWCNT due to its quasi-one-dimensional structure. The frequency and life time of optical phonon modes are also studied at different temperatures. In particular, the life time of the in-plane optical phonons in graphene and the axial optical phonon in SWCNT can be described by an uniform formula $\tau (T)=560/T$, which coincides with the experimental results., Comment: 8 pages, 9 figures

The nonequilibrium Green's function method is applied to investigate the coefficient of thermal expansion (CTE) in single-walled carbon nanotubes (SWCNT) and graphene. It is found that atoms deviate about 1% from equilibrium positions at T=0 K, resulting from the interplay between quantum zero-point motion and nonlinear interaction. The CTE in SWCNT of different sizes is studied and analyzed in terms of the competition between various vibration modes. As a result of this competition, the axial CTE is positive in the whole temperature range, while the radial CTE is negative at low temperatures. In graphene, the CTE is very sensitive to the substrate. Without substrate, CTE has large negative region at low temperature and very small value at high temperature limit, and the value of CTE at T=300 K is $-6\times 10^{-6}$ K$^{-1}$ which is very close to recent experimental result, $-7\times 10^{-6}$ K$^{-1}$ (Nat. Nanotechnol. \textbf{10}, 1038 (2009)). A very weak substrate interaction (about 0.06% of the in-plane interaction) can largely reduce the negative CTE region and greatly enhance the value of CTE. If the substrate interaction is strong enough, the CTE will be positive in whole temperature range and the saturate value at high temperature reaches $2.0\times 10^{-5}$ K$^{-1}$., Comment: final version, to appear in PRB

A generalized Langevin equation with quantum baths (QMD) for thermal transport is derived with the help of nonequilibrium Green's function (NEGF) formulation. The exact relationship of the quasi-classical approximation to NEGF is demonstrated using Feynman diagrams of the nonlinear self energies. To leading order, the retarded self energies agree, but QMD and NEGF differ in lesser/greater self energies. An implementation for general systems using Cholesky decomposition of the correlated noises is discussed. Some means of stabilizing the dynamics are given. Thermal conductance results for graphene strips under strain and temperature dependence of carbon nanotubes are presented. The "quantum correction" method is critically examined., Comment: 9 pages, 9 figures

The results of the experiments showed that biological contact A/O process could run steadily under low temperature and had better removal effect for ammonia nitrogen and had some removal effect for COD and TN from water of Guanting Reservoir. When the temperature dropped greatly, removal ratio of ammonia nitrogen dropped evidently, but gradually rose and remained at high removal level at last. Under the conditions of the experiment that the temperature was 0-5 degrees C and influent ammonia nitrogen was about 10 mg/L, ammonia nitrogen removal rate remained more than 95% at last. The change of temperature had no evident influence on removal effect of COD. And the conclusion could be got by microscope that under the temperature at 0-5 degrees C the microorganism in the biofilm still had a good activity.

New compounds (COOCH2C2H-m)2[Co2(CO)6]2 1, (HC2CH2O(O)CCOOCH2C2H-μ) [Co2(CO)6] 2, (COOCH2C2H-μ)2[RuCo2(CO)9][Co2(CO)6] 3 and (COOCH2C2H-μ)2[RuCo2(CO)9]2 4 were prepared by the reaction of (COOCH2C2H)2 with Co2(CO)8 and RuCo2(CO)11, and the structure of 1 has been established by single-crystal X-ray diffraction methods.