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Beijing Computational Science Research CenterBeijing

Beijing, China
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Seshadreesan K.P.,Louisiana State University | Dowling J.P.,Louisiana State University | Dowling J.P.,Beijing Computational Science Research CenterBeijing | Agarwal G.S.,Oklahoma State University
Physica Scripta | Year: 2015

In continuous-variable quantum information, non-Gaussian entangled states that are obtained from Gaussian entangled states via photon subtraction are known to contain more entanglement. This makes them better resources for quantum information processing protocols, such as, quantum teleportation. We discuss the teleportation of non-Gaussian, non-classical Schrödinger-cat states of light using two-mode squeezed vacuum light that is made non-Gaussian via subtraction of a photon from each of the two modes. We consider the experimentally realizable cat states produced by subtracting a photon from the single-mode squeezed vacuum state. We discuss two figures of merit for the teleportation process, (a) the fidelity, and (b) the maximum negativity of the Wigner function at the output. We elucidate how the non-Gaussian entangled resource lowers the requirements on the amount of squeezing necessary to achieve any given fidelity of teleportation, or to achieve negative values of the Wigner function at the output. © 2015 The Royal Swedish Academy of Sciences.

Wang Y.,Jilin University | Wang H.,Jilin University | Wang H.,University of Saskatchewan | Tse J.S.,Jilin University | And 5 more authors.
Physical Chemistry Chemical Physics | Year: 2015

It is now known that the structure and properties of a material can be significantly altered under extreme compression. In this work, a structural search was performed to investigate the phase stabilities and structures of SrH2n (n = 1-5) in the pressure range of 50-300 GPa. The high-pressure polymorphs reveal a variety of hydrogen structural units ranging from monatomic hydride to linear and bent H3 and spiral polymer chains. A novel graphene like H-layer structure was found to exist in SrH10 at 300 GPa. The structural diversity in the predicted high pressure structures provides an opportunity for an in-depth analysis of the chemical bonding in the high pressure polyhydrides. It is shown from theoretical calculations that the electronegativity of molecular hydrogen is similar to that of group 13 and 14 elements. This resulted in electrons being transferred from Sr to the hydrogen molecules. Thus, a consideration of the number of valence electrons available from Sr that can be shared among the H2 serves as a useful guide to rationalize the structures of the H-moieties. An alternative description of the high pressure structures differing from a previous study is presented here. This journal is © the Owner Societies.

Liu W.,Jilin University | Miao M.,California State University, Northridge | Miao M.,Beijing Computational Science Research CenterBeijing | Liu J.-Y.,Jilin University
Journal of Materials Chemistry C | Year: 2015

Two-dimensional (2D) semiconductor materials and the fabrication of related devices have become a new focus of electronics and materials science recently. Compared with three-dimensional (3D) semiconductors, the choice of 2D materials is very limited. Recently, the emerging goal of fabricating functional heterojunctions of 2D semiconductors has spurred a strong need to search for 2D materials that have a large variety of band gaps and band edges. Here, we propose a single layer of B2S3 as a new potential 2D material, conceived directly from its existing layered 3D crystal. Using an advanced hybrid functional method, we demonstrated that 2D B2S3 has a gap of 3.75 eV, filling a missing energy range for 2D materials. Furthermore, by adding extra B atoms at the 'vacancy' sites of the B2S3 structure to give a 1 : 1 stoichiometry, we constructed new 2D BN and graphene allotropes that show large variation in the electronic structure. The BN allotrope exhibits a gap that is 0.99 eV lower than h-BN. Although the structure is significantly different to graphene, the new C allotrope contains a Dirac cone. However, the Dirac point is slightly lower than the Fermi level because of the electron transfer from an adjacent valence band to the Dirac cone states, resulting in a metallic state with both 'massless' electrons and massive holes. © The Royal Society of Chemistry.

Meng L.,Xiamen University | Yam C.,Beijing Computational Science Research CenterBeijing | Yam C.,University of Hong Kong | Zhang Y.,University of Hong Kong | And 3 more authors.
Journal of Physical Chemistry Letters | Year: 2015

The unique optical properties of nanometallic structures can be exploited to confine light at subwavelength scales. This excellent light trapping is critical to improve light absorption efficiency in nanoscale photovoltaic devices. Here, we apply a multiscale quantum mechanics/electromagnetics (QM/EM) method to model the current-voltage characteristics and optical properties of plasmonic nanowire-based solar cells. The QM/EM method features a combination of first-principles quantum mechanical treatment of the photoactive component and classical description of electromagnetic environment. The coupled optical-electrical QM/EM simulations demonstrate a dramatic enhancement for power conversion efficiency of nanowire solar cells due to the surface plasmon effect of nanometallic structures. The improvement is attributed to the enhanced scattering of light into the photoactive layer. We further investigate the optimal configuration of the nanostructured solar cell. Our QM/EM simulation result demonstrates that a further increase of internal quantum efficiency can be achieved by scattering light into the n-doped region of the device. © 2015 American Chemical Society.

Guo G.-C.,Xiangtan University | Guo G.-C.,Beijing Computational Science Research CenterBeijing | Wang D.,Beijing Computational Science Research CenterBeijing | Wei X.-L.,Xiangtan University | And 6 more authors.
Journal of Physical Chemistry Letters | Year: 2015

There is a great desire to develop the high-efficient anodes materials for Li batteries, which require not only large capacity but also high stability and mobility. In this work, the phosphorene/graphene heterostructure (P/G) was carefully explored based on first-principles calculations. The binding energy of Li on the pristine phosphorene is relatively weak (within 1.9 eV), whereas the phosphorene/graphene heterostructure (P/G) can greatly improve the binding energy (2.6 eV) without affecting the high mobility of Li within the layers. The electronic structures show that the large Li adsorption energy and fast diffusion ability of the P/G origin from the interfacial synergy effect. Interestingly, the P/G also displays ultrahigh stiffness (Cac = 350 N/m, Czz = 464 N/m), which can effectively avoid the distortion of the pristine phosphorene after the insertion of lithium. Thus, P/G can greatly enhance the cycle life of the battery. Owing to the high capacity, good conductivity, excellent Li mobility, and ultrahigh stiffness, P/G is a very promising anode material in Li-ion batteries (LIBs). © 2015 American Chemical Society.

Zhang Y.N.,Chengdu Green Energy And Green Manufacturing Technology | Zhang Y.N.,Beijing Computational Science Research CenterBeijing | Zhang Y.N.,University of California at Irvine | Law M.,University of California at Irvine | Wu R.Q.,University of California at Irvine
Journal of Physical Chemistry C | Year: 2015

Through density functional calculations, we investigated the diffusion of isolated sulfur vacancies (VS) from the bulk of iron pyrite (cubic FeS2) to the (100) and (111) surfaces. The influence of vacancy depth on the vacancy formation energy and the activation energy for vacancy diffusion are discussed. Significantly, we find that VS defects tend to migrate toward stoichiometric and sulfur-rich surfaces through sequential "intra-dimer" and "inter-dimer" hops. We find a pre-exponential constant (D0) of 9 × 10-7 m2 s-1 and an activation energy (E) of 1.95 eV for sulfur vacancy diffusion in bulk pyrite, corresponding to a vacancy diffusion coefficient DV = D0 exp(-E/kT) = 9 × 10-40 m2 s-1 at 25 °C and 5 × 10-18 m2 s-1 at 600 °C. The activation energy is smaller near the surface (e.g., E = 1.5 eV near the stoichiometric (100) surface), resulting in faster vacancy diffusion near the surface than in the bulk. Using the formation enthalpy of VS at the (100) surface, E = 2.37 eV, we find a sulfur diffusivity in bulk pyrite DS = 7 × 10-47 m2 s-1 at 25 °C and 2 × 10-20 m2 s-1 at 600 °C. The calculated DS values are in reasonable agreement with experiment only at intermediate temperatures (∼275-625 °C). Our results show that bulk and near-surface sulfur vacancies can be healed in sulfur-rich conditions at reasonably high temperatures. The mechanism of vacancy diffusion presented here should be useful in managing VS defects during the fabrication of high-quality pyrite samples for solar energy conversion applications. © 2015 American Chemical Society.

Jiang N.,Chinese University of Hong Kong | Ruan Q.,Chinese University of Hong Kong | Qin F.,Chinese University of Hong Kong | Wang J.,Chinese University of Hong Kong | Lin H.-Q.,Beijing Computational Science Research CenterBeijing
Nanoscale | Year: 2015

Active modulation of the plasmon coupling in homodimers of polyaniline (PANI)-coated Au nanospheres is achieved by changing the proton-doping state of the PANI shell. Such a PANI-enabled modulation of the plasmon coupling in the dimers gives rise to remarkable spectral shifts, which show an exponential dependence on the interparticle gap distance. For the dimer with a 10 nm PANI shell thickness and a 0.5 nm gap distance, the shift of the stronger scattering peak in response to the active modulation reaches 231 nm. Electrodynamic simulations reveal that the shift of the dipolar bonding plasmon mode dominates the position variation of the stronger scattering peak for the dimers with different gap distances. Moreover, the quadrupolar bonding plasmon mode can be turned on and off by controlling the proton-doping state of the dimers with gap distances of less than ∼3 nm. These results are of high importance for fundamentally understanding the sensitivity of coupled plasmon resonance modes to the dielectric environment, as well as for designing active plasmonic devices with high modulation performances. This journal is © The Royal Society of Chemistry.

Zhao R.,Beijing Computational Science Research CenterBeijing | Zhao R.,Henan Polytechnic University | Zhao R.,CAS Beijing National Laboratory for Molecular | Li F.,Henan Polytechnic University | And 3 more authors.
Physical Chemistry Chemical Physics | Year: 2015

Edge structure and stability are crucial in determining both the morphology and the growth behaviours of hexagonal boron nitride (h-BN) domains in chemical vapour deposition (CVD) growth under near thermal equilibrium conditions. In this study, various edges of h-BN on three typical transition metal surfaces used for h-BN's CVD growth, Cu(111), Ni(111) and Rh(111), are explored with density functional theory calculations. Different from that in vacuum, our study shows that the formation of non-hexagonal rings, such as pentagon, heptagon or their pairs, is energetically not preferred and both zigzag (ZZ) edges are more stable than the armchair (AC) edge on all the explored catalyst surfaces under typical conditions of h-BN's CVD growth, which explains the broad experimental observation of triangular h-BN domains. More importantly, our results indicate that, instead of the pristine ZZ edge terminated with nitrogen atoms (ZZN), the triangular BN domains observed in experiments are likely to be enclosed with ZZ Klein edges having dangling atoms, ZZB + N or ZZN + B. By applying the theory of Wulff construction, we predicted that the equilibrium shape of a BN domain could be a hexagon enclosed with nitrogen-rich AC edges, triangles enclosed with two different types of ZZ Klein edges or a hexagon enclosed with boron-rich AC edges if the growth is in a N-rich, neutral or B-rich environment, respectively. This study presents how the edges and equilibrium shapes of h-BN domains can be controlled during the CVD synthesis and provides guidelines for further exploring the growth behaviours and improving the quality of CVD-prepared h-BN films. This journal is © the Owner Societies.

Tang L.,Dalian Nationalities University | Shi R.,Dalian University of Technology | Su Y.,Dalian University of Technology | Zhao J.,Dalian University of Technology | Zhao J.,Beijing Computational Science Research CenterBeijing
Journal of Physical Chemistry A | Year: 2015

In order to understand the cage fusion behavior during the nucleation processes of methane hydrate (MH), methane-encapsulated double-cage clusters (CH4)2(H2O)n (n = 30-43) and several multicage structures with three or more cages were studied employing DFT-D methods. We find that almost all the lowest-energy double-cage structures can be constructed by merging the most stable structures of the monocage clusters CH4(H2O)n (n = 18-24). Double-cage structures can achieve higher stability through sharing a hexagon than a pentagon, which may be applicable to larger fused cage clusters. The preference of hexagons during cage fusion should be favorable for the appearance of the cages including hexagons such as the 51262, 51264 cages during the MH nucleation process. The symmetric C-H stretching modes of methane molecules in the double-cage structures show a clear trend of red shift with increasing size of the composing monocages. Compared with the case of monocages, the stretching frequencies of methane molecules in double-cage structures shift slightly, indicating variation of monocage configuration when cage fusion occurs. The larger multicage structures are found to possess higher fusion energies through sharing more polygons. Their thermodynamic stabilities do not simply increase with the number of fused monocages and are affected by the spatial arrangement of the building cages. © 2015 American Chemical Society.

Zhang H.,Shenyang University | Zhang H.,Beijing Computational Science Research CenterBeijing | Lin X.,Shenyang University | Tang Z.-K.,Beijing Computational Science Research CenterBeijing
Solid State Communications | Year: 2015

Abstract The layered ScS2 nanostructures are investigated by the first-principles calculations. Single-layer 2D H-ScS2 and T-ScS2 are demonstrated as free-standing stable by phonon spectrum. In addition, their electronic structures and magnetic properties differ from the bulk counterparts and depend on crystal structure types. For example, single-layer H-ScS2 becomes ferromagnetic and semiconducting from nonmagnetic and metallic bulk 2H-ScS2. More interestingly, the electronic structures and magnetic properties of ScS2 can be further modulated from 1D nanoribbons. The present calculations explore novel low-dimensional ScS2 nanostructures as promising candidates of electronic and magnetic devices. © 2015 Elsevier Ltd.

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