C. Z. Wang

Zhejiang University, Hang-hsien, Zhejiang Sheng, China

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Publications (245)630.45 Total impact

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    ABSTRACT: We present an efficient \textit{ab initio} method for calculating the electronic structure and total energy of strongly correlated electron systems. The method extends the traditional Gutzwiller approximation for one-particle operators to the evaluation of the expectation values of two particle operators in a full many-electron Hamiltonian. The method is free of adjustable Coulomb parameters, and has no double counting issues in the calculation of total energy, and has the correct atomic limit. We demonstrate that the method describes well the bonding and dissociation behaviors of the hydrogen and nitrogen clusters. We also show that the method can satisfactorily tackle great challenging problems faced by the density functional theory recently discussed in the literature. The computational workload of our method is similar to the Hartree-Fock approach while the results are comparable to high-level quantum chemistry calculations.
    06/2014;
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    ABSTRACT: Solving the crystal structures of novel phases with nanoscale dimensions resulting from rapid quenching is difficult due to disorder and competing polymorphic phases. Advances in computer speed and algorithm sophistication have now made it feasible to predict the crystal structure of an unknown phase without any assumptions on the Bravais lattice type, atom basis, or unit cell dimensions, providing a novel approach to aid experiments in exploring complex materials with nanoscale grains. This approach is demonstrated by solving a long-standing puzzle in the complex crystal structures of the orthorhombic, rhombohedral, and hexagonal polymorphs close to the Zr2Co11 intermetallic compound. From our calculations, we identified the hard magnetic phase and the origin of high coercivity in this compound, thus guiding further development of these materials for use as high performance permanent magnets without rare-earth elements.
    Physical Review Letters 01/2014; 112(4):045502. · 7.73 Impact Factor
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    ABSTRACT: Reverse Monte Carlo simulations (RMC) have been widely used to generate three dimensional (3D) atomistic models for glass systems. To examine the reliability of the method for metallic glass, we use RMC to predict the atomic configurations of a "known" structure from molecular dynamics (MD) simulations, and then compare the structure obtained from the RMC with the target structure from MD. We show that when the structure factors and partial pair correlation functions from the MD simulations are used as inputs for RMC simulations, the 3D atomistic structure of the glass obtained from the RMC gives the short- and medium-range order in good agreement with those from the target structure by the MD simulation. These results suggest that 3D atomistic structure model of the metallic glass alloys can be reasonably well reproduced by RMC method with a proper choice of input constraints.
    01/2014; 115(5).
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    ABSTRACT: The local atomic structure evolution in Al2Au alloy during solidification from 2000 K to 400 K was studied by ab initio molecular dynamics simulations and analyzed using the structure factor, pair correlation functions, bond angle distributions, the Honeycutt–Anderson (HA) index and Voronoi tessellation methods. It was found that the icosahedral-like clusters are negligible in the Al2Au stable liquid and supercooled liquid states, and the most abundant clusters are those having HA indices of 131 and 120 or Voronoi indices of 〈0, 4, 4, 0〉, 〈0, 3, 6, 0〉 and 〈0, 4, 4, 2〉 with coordination numbers of 8, 9 and 10, respectively. These clusters are similar to the local atomic structures in the CaF2-type Al2Au crystal, revealing the existence of structure heredity between liquid and crystalline phase in Al2Au alloy.
    Acta Materialia. 01/2014; 68:1–8.
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    Journal of Non-Crystalline Solids 01/2014; · 1.72 Impact Factor
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    ABSTRACT: The temperature dependent optical properties of tin film from solid to liquid were studied by spectroscopic ellipsometry and ab initio molecular dynamics simulations. The dielectric function of liquid Sn was different from solid, and an interband transition near 1.5 eV was easily observed in solid while it apparently disappeared upon melting. From the evolution of optical properties with temperature, an optical measurement to acquire the melting point by ellipsometry was presented. From first principles calculation, we show that the local structure difference in solid and liquid is responsible for this difference in the optical properties observed in experiment.
    Applied Physics Letters 01/2014; 104(12):121907-121907-5. · 3.79 Impact Factor
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    ABSTRACT: The structure of the orthorhombic Zr2Co11 phase was revisited in the present work. Selected-area electron diffraction (SAED) and high-resolution electron microscopy (HREM) techniques were used to investigate the structure. They show the orthorhombic Zr2Co11 phase has a 1-D incommensurate modulated structure. The structure can be approximately described as a B-centered orthorhombic lattice. The lattice parameters of the orthorhombic Zr2Co11 phase have been determined by a tilt series of SAED patterns. A hexagonal network with a modulation wave has been observed in the HREM image and the hexagonal motif is considered as the basic structural unit.
    Journal of Alloys and Compounds 01/2014; 611:167–170. · 2.73 Impact Factor
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    ABSTRACT: We present a genetic algorithm (GA) for structural search that combines the speed of structure exploration by classical potentials with the accuracy of density functional theory (DFT) calculations in an adaptive and iterative way. This strategy increases the efficiency of the DFT-based GA by several orders of magnitude. This gain allows a considerable increase in the size and complexity of systems that can be studied by first principles. The performance of the method is illustrated by successful structure identifications of complex binary and ternary intermetallic compounds with 36 and 54 atoms per cell, respectively. The discovery of a multi-TPa Mg-silicate phase with unit cell containing up to 56 atoms is also reported. Such a phase is likely to be an essential component of terrestrial exoplanetary mantles.
    Journal of Physics Condensed Matter 12/2013; 26(3):035402. · 2.22 Impact Factor
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    ABSTRACT: Atomic structure transitions of liquid niobium during solidification, at different temperatures from 3200 to 1500 K, were studied by using ab initio molecular dynamics simulations. The local atomic structure variations with temperature are investigated by using the pair-correlation function, the structure factor, the bond-angle distribution function, the Honeycutt-Anderson index, Voronoi tessellation and the cluster alignment methods. Our results clearly show that, upon quenching, the icosahedral short-range order dominates in the stable liquid and supercooled liquid states before the system transforms to crystalline body-center cubic phase at a temperature of about 1830 K.
    Journal of Physics Condensed Matter 12/2013; 26(5):055004. · 2.22 Impact Factor
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    ABSTRACT: The effects of strontium modification on the structure and dynamics of Al88Si12 liquid are studied by means of ab initio molecular dynamics simulations. By replacing 0.5% and 4.0% of Al with Sr, we show that the addition of Sr lowers the self-diffusion of Al and Si of the liquid and reduces the nearest-neighbor correlation between Si atoms. The simulation provides an explanation for the change in morphology of the eutectic phases observed in rapidly solidified Al-Si alloys modified with Sr.
    Journal of Physics Condensed Matter 05/2013; 25(24):245102. · 2.22 Impact Factor
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    ABSTRACT: Triangular graphene nanoflakes (GNFs) embedded in fluorinated graphene are systematically investigated using first-principles density functional theory (DFT) calculations. The electronic and magnetic properties of such nanoflakes depend sensitively on the topology (armchair or zigzag) and the length of the edge of nanofakes. All embedded armchair triangular GNFs are semiconducting with size-dependent band gaps. The embedded zigzag triangular GNFs are magnetic with a ferrimagnetic ground state due to topological frustration of the π bonds. The magnetic moment scales linear with the size of the triangular GNF.
    Chemical Physics Letters 05/2013; 572:48–52. · 2.15 Impact Factor
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    ABSTRACT: Electronic structures of (4, n) and (m, 4) (the NW has m layers parallel to the {1 1 1} facet and n layers parallel to {1 1 0}) Si/Ge core/shell nanowires (NWs) along the [1 1 2] direction with cross-sectional aspect ratio (m/n) from 0.36 to 2.25 are studied by first-principles calculations. An indirect to direct band gap transition is observed as m/n decreases, and the critical values of m/n and diameter for the transition are also estimated. The size of the band gap also depends on the aspect ratio. These results suggest that m/n plays an important role in modulating the electronic properties of the NWs.
    Journal of Physics D Applied Physics 04/2013; 46(13):135302. · 2.53 Impact Factor
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    ABSTRACT: Structural and electronic properties, including deformation, magnetic moment, Mulliken population, bond order, as well as electronic transport properties, of zigzag graphene nanoribbon (ZGNR) with Co adatoms on hollow sites are investigated by quasi-atomic minimal basis orbits (QUAMBOs), a first-principles tight binding (TB) scheme based on density functional theory (DFT), combined with a non-equilibrium Green's function. For electronic transport, below the Fermi level the transmission is strongly suppressed and spin dependent as a result of magnetism by Co adatom adsorption, while above the Fermi level the transmission is slightly distorted and spin independent. Due to the local environment dependence of QUAMBOs-TB parameters, we construct QUAMBOs-TB parameters of ZGNR leads and ZGNR with Co adatoms on hollow center sites by a divide-and-conquer approach, and accurately reproduce the electronic transmission behavior. Our QUAMBO-NEGF method is a new and promising way of examining electronic transport in large-scale systems.
    Journal of Physics Condensed Matter 03/2013; 25(10):105302. · 2.22 Impact Factor
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    ABSTRACT: The recently introduced correlation matrix renormalization approximation (CMRA) was further developed by adopting a completely factorizable form for the renormalization z-factors, which assumes the validity of the Wick's theorem with respect to Gutzwiller wave function. This approximation (CMR-II) shows better dissociation behavior than the original one (CMR-I) based on the straightforward generalization of the Gutzwiller approximation to two-body interactions. We further improved the performance of CMRA by redefining the z-factors as a function of f(z) in CMR-II, which we call CMR-III. We obtained an analytical expression of f(z) by enforcing the equality in energy functional between CMR-III and full configuration interaction for the benchmark minimal basis H2. We show that CMR-III yields quite good binding energies and dissociation behaviors for various hydrogen clusters with converged basis set. Finally, we apply CMR-III to hydrogen crystal phases and compare the results with quantum Monte Carlo.
    03/2013; 89(4):24003-.
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    ABSTRACT: In the present study, we compare the structure of NiZr2 and CuZr2 disordered (liquid and amorphous) alloys. While Cu and Ni have similar atomic radii, the formation heats of these alloys differ by more than a factor of two. Moreover, the most stable crystal phase in the CuZr2 alloy has the C11b lattice while the most stable phase in the NiZr2 alloy has the C16 lattice. Comparing these two alloys allows us to directly explore how the chemistry and atomic size affect the disordered phase structure. We find that all differences in the structures of the disordered alloys are readily explained by the smaller Ni–Zr separation driven by the higher heat of mixing and the structure of the disordered alloys does not necessarily resemble the local packing structure of their crystalline counterparts. Comparison of the disordered alloys and their most stable crystal phase structures explains the better glass formability of the CuZr2 alloy.
    Philosophical Magazine A 11/2012; 92(33):4098-4112.
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    ABSTRACT: First-principles calculations were performed to study the structure and stability of the Al46 cluster. The results suggest two competing structural motifs, the spherical endohedral cage and layer-stacking structures. It is shown that although medium-sized Al clusters tend to form layered structures (i.e., fcc fragments with a stacking fault), a spherical endohedral cage configuration is also an important structural motif for the magic Al46 cluster. Besides, the cluster ions were also studied, and the calculated PES of the Al46- isomer with the minimum of free energy is in better agreement with the experimental PES data.
    Chemical Physics Letters 10/2012; 549:44–50. · 2.15 Impact Factor
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    ABSTRACT: We report a collection of lowest-energy structures of hydrocarbon molecules CnHm (n = 6-18, m = 0 - 2n + 2) within the wide hydrogen chemical potential range. The genetic algorithm combined with Brenner's empirical potential is applied for the search. The resultant low-energy structures are further examined by ab initio quantum chemical calculations. The lowest-energy molecules with several additional low-energy structures are classified to four groups according to their structural motifs and the phase diagram with respect to carbon atom number and hydrogen chemical potential is presented. The results provide useful information for identifying the hydrocarbon molecules in the interstellar medium as well as addressing the hydrocarbon-related nanofragment growth in experiments.
    Nano LIFE. 07/2012; 02(02).
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    ABSTRACT: The understanding of metal nucleation on graphene is essential for promising future applications, especially of magnetic metals which can be used in spintronics or computer storage media. A common method to study the grown morphology is to measure the nucleated island density n as a function of growth parameters. Surprisingly, the growth of Fe on graphene is found to be unusual because it does not follow classical nucleation: n is unexpectedtly high, it increases continuously with the deposited amount θ and shows no temperature dependence. These unusual results indicate the presence of long range repulsive interactions. Kinetic Monte Carlo simulations and density functional theory calculations support this conclusion. In addition to answering an outstanding question in epitaxial growth, i.e., to find systems where long range interactions are present, the high density of magnetic islands, tunable with θ, is of interest for nanomagnetism applications.
    Physical Review Letters 07/2012; 109(2):026103. · 7.73 Impact Factor
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    ABSTRACT: We present a systematic study of metal adatom adsorption on graphene by ab initio calculations. The calculations cover alkali metals, sp-simple metals, 3d and group 10 transition metals, noble metals, as well as rare earth metals. The correlation between the adatom adsorption properties and the growth morphology of the metals on graphene is also investigated. We show that the growth morphology is related to the ratio of the metal adsorption energy to its bulk cohesive energy (E(a)/E(c)) and the diffusion barrier (ΔE) of the metal adatom on graphene. Charge transfer, electric dipole and magnetic moments, and graphene lattice distortion induced by metal adsorption would also affect the growth morphologies of the metal islands. We also show that most of the metal nanostructures on graphene would be thermally stable against coarsening.
    Physical Chemistry Chemical Physics 05/2012; 14(25):9157-66. · 3.83 Impact Factor
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    ABSTRACT: Short-range order in liquid and amorphous structures of Cu80Si20 is studied by ab initio molecular dynamics simulations. We performed the simulations at 1140 and 300 K respectively to investigate the local structure change from liquid to amorphous. The result of structure factor in comparison with experimental data indicates that our simulation of amorphous Cu80Si20 is reliable. By using the bond-angle distribution function, Honeycutt–Andersen index, Voronoi tessellation method, and the atomistic cluster alignment method, the icosahedral short-range order in the system is revealed. Strong Cu–Si interaction was also observed.
    Intermetallics 04/2012; 30:122–126. · 1.86 Impact Factor

Publication Stats

3k Citations
630.45 Total Impact Points

Institutions

  • 2014
    • Zhejiang University
      • State Key Lab of Silicon Materials
      Hang-hsien, Zhejiang Sheng, China
  • 1991–2014
    • Iowa State University
      • • Ames Laboratory
      • • Department of Physics and Astronomy
      • • Department of Chemistry
      Ames, Iowa, United States
  • 2011–2013
    • Renmin University of China
      • Department of Physics
      Beijing, Beijing Shi, China
    • Karlsruhe Institute of Technology
      • Institut für Theorie der Kondensierten Materie
      Eggenstein-Leopoldshafen, Baden-Wuerttemberg, Germany
    • University of Science and Technology of China
      • Department of Physics
      Hefei, Anhui Sheng, China
  • 2005–2013
    • Fudan University
      • Department of Optical Science and Engineering
      Shanghai, Shanghai Shi, China
  • 2010–2011
    • U.S. Department of Energy
      • Ames Lab
      Washington, Washington, D.C., United States
    • Qingdao University
      • College of Physics
      Tsingtao, Shandong Sheng, China
  • 2005–2011
    • Jilin University
      • State Key Lab of Theoretical and Computational Chemistry
      Jilin, Jilin Sheng, China
  • 2006
    • Northeast Normal University
      Hsin-ching, Jilin Sheng, China
  • 2004–2005
    • Seoul National University
      • Department of Materials Science and Engineering
      Seoul, Seoul, South Korea
    • Colorado School of Mines
      • Department of Mining Engineering
      Golden, CO, United States