C. Z. Wang

U.S. Department of Energy, Washington, Washington, D.C., United States

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Publications (266)752.92 Total impact

  • Yuxiang Huang · Li Huang · C. Z. Wang · M. J. Kramer · K. M. Ho ·

    Journal of Applied Physics 11/2015; 118(19):195902. DOI:10.1063/1.4935877 · 2.18 Impact Factor
  • Li-Zhen Zhao · Wen-Cai Lu · Wan-Sheng Su · Wei Qin · C. Z. Wang · K. M. Ho ·
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    ABSTRACT: We performed first-principles calculations to study the structural stability of Si78 clusters with or without hydrogen passivation. The calculations reveal that an endohedral double cage isomer is more stable than the diamond-like structure, whereas the opposite is found for the hydrogen passivated isomers. In particular, the hydrogenated double cage and diamond-like structure may display blue shifts to the visible and UV regions, respectively. The IR vibration spectra, ionization potential (IP) and electronic density-of-states of the clusters were calculated and discussed.
    Physical Chemistry Chemical Physics 10/2015; 17(41). DOI:10.1039/C5CP03856A · 4.49 Impact Factor
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    Y. X. Yao · J. Liu · C. Liu · W. C. Lu · C. Z. Wang · K. M. Ho ·
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    ABSTRACT: We present an efficient 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 the 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, as well as the ammonia composed of hydrogen and nitrogen atoms. 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.
    Scientific Reports 08/2015; 5:13478. DOI:10.1038/srep13478 · 5.58 Impact Factor
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    ABSTRACT: The phonon properties, electronic structures and optical properties of novel carbon allotropes, such as monolayer penta-graphene (PG), double-layer PG and T12-carbon, were explored by means of first-principles calculations. Results of phonon calculations demonstrate that these exotic carbon allotropes are dynamically stable. In addition, the bulk T12 phase is an indirect-gap semiconductor having a bandgap of ~4.89 eV. Whereas the bulk material transforms to a 2D phase, the monolayer and double-layer PG become quasi-direct gap semiconductors with smaller band gaps of ~2.64 eV and ~3.27eV, respectively. Furthermore, the partial charge density analysis indicates that the 2D phases retain part of the electronic characteristics of the T12 phase. The linear photon energy-dependent dielectric functions and related optical properties including refractive index, extinction coefficient, absorption spectrum, reflectivity, and energy loss spectrum were also computed and discussed. The structural estimation obtained as well as other findings are in agreement with existing theoretical data. The calculated results are beneficial to the practical applications of these exotic carbon allotropes in optoelectronics and electronics.
  • Wen-Cai Lu · C. Z. Wang · Li-Zhen Zhao · Wei Qin · K. M. Ho ·
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    ABSTRACT: A tight-binding potential model which goes beyond the Slater-Koster two-center approximation and includes explicit three-center and crystal field expressions is presented. Using carbon and silicon as examples, we show that various bulk structures, surface reconstructions, and the structures of clusters and liquids of C and Si can be well described by the present three-center tight-binding model. These results demonstrate that three-center interaction and crystal field effect are very important for improving the transferability of tight-binding models in describing the structures and properties of materials over a broad range of bonding configurations.
    Physical Review B 07/2015; 92(3). DOI:10.1103/PhysRevB.92.035206 · 3.74 Impact Factor
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    ABSTRACT: The structures and dynamics of liquid Ag74Ge26 alloy at different temperatures were investigated by high-energy X-ray diffraction and ab initio molecular dynamics simulation. The calculated structure factors agree well with the experimental data. Local atomic structure orders have been characterized by angular distribution functions, Honeycutt-Andersen index, Voronoi tessellation and the atomic cluster alignment. We reveal that (i) 〈0, 3, 6, 4, 0〉, 〈0, 2, 8, 4, 0〉, 〈0, 3, 6, 5, 0〉, and 〈1, 3, 4, 5, 1〉 polyhedral dominate in the undercooled Ag74Ge26 liquid. (ii) The icosahedral-like short-range order is enhanced as the temperature decreases while 〈0, 3, 6, 4, 0〉, 〈0, 2, 8, 4, 0〉, 〈0, 3, 6, 5, 0〉, and 〈0, 1, 10, 2, 0〉 polyhedral become the major short-range orders at low temperature. (iii) The medium-range order which was formed for amorphous phase at ambient temperature persists in the undercooled liquid. In addition, it is found that the diffusion constant of Ag is lower than that of Ge over the studied temperature range. Our findings elucidate that highly dominated short-range order associated with nearest-neighbors shell could empower the development of medium-range order and the formation of metallic glasses.
    Acta Materialia 06/2015; 92. DOI:10.1016/j.actamat.2015.03.047 · 4.47 Impact Factor
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    T Wang · F Zhang · L Yang · X W Fang · S H Zhou · M J Kramer · C Z Wang · K M Ho · R E Napolitano ·
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    ABSTRACT: Liquid phase diffusion plays a critical role in phase transformations (e.g. glass transformation and devitrification) observed in marginal glass forming systems such as Al-Sm. Controlling transformation pathways in such cases requires a comprehensive description of diffusivity, including the associated composition and temperature dependencies. In the computational study reported here, we examine atomic diffusion in Al-Sm liquids using ab initio molecular dynamics (AIMD) and determine the diffusivities of Al and Sm for selected alloy compositions. Non-Arrhenius diffusion behavior is observed in the undercooled liquids with an enhanced local structural ordering. Through assessment of our AIMD result, we construct a general formulation for Al-Sm liquid, involving a diffusion mobility database that includes composition and temperature dependence. A Volmer-Fulcher-Tammann (VFT) equation is adopted for describing the non-Arrhenius behavior observed in the undercooled liquid. The composition dependence of diffusivity is found quite strong, even for the Al-rich region contrary to the sole previous report on this binary system. The model is used in combination with the available thermodynamic database to predict specific diffusivities and compares well with reported experimental data for 0.6 at.% and 5.6 at.% Sm in Al-Sm alloys.
    Scientific Reports 06/2015; 5:10956. DOI:10.1038/srep10956 · 5.58 Impact Factor
  • M I Mendelev · F Zhang · Z Ye · Y Sun · M C Nguyen · S R Wilson · C Z Wang · K M Ho ·
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    ABSTRACT: A semi-empirical potential for the Al 90 Sm 10 alloy is presented. The potential provides satisfactory reproduction of pure Al properties, the formation energies of a set of Al–Sm crystal phases with Sm content about 10%, and the structure of the liquid Al 90 Sm 10 alloy. During molecular dynamics simulation in which the liquid alloy is cooled at a rate of 10 10 K s −1 , the developed potential produces a glass structure with lower ab initio energy than that produced by ab initio molecular dynamics (AIMD) itself using a typical AIMD cooling rate of 8·10 13 K s −1 . Based on these facts the developed potential should be suitable for simulations of phase transformations in the Al 90 Sm 10 alloy.
    Modelling and Simulation in Materials Science and Engineering 06/2015; 23(4-4):045013. DOI:10.1088/0965-0393/23/4/045013 · 2.17 Impact Factor
  • Wei Qin · W.-C. Lu · L.-H. Xia · L.-Z. Zhao · Q.-J. Zang · C.Z. Wang · K.M. Ho ·
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    ABSTRACT: The lowest-energy structures of neutral and cationic GenM (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge9 and Ge10 clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Gen clusters. However, the neutral and cationic FeGe9,10,MnGe9,10 and Ge10Al are cage-like with the metal atom encapsulated inside. Such cage-like transition metal doped Gen clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge9,10Fe and Ge9Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.
    AIP Advances 06/2015; 5(6). DOI:10.1063/1.4923316 · 1.52 Impact Factor
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    Y. Zhang · C. Z. Wang · M. I. Mendelev · F. Zhang · M. J. Kramer · K. M. Ho ·
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    ABSTRACT: Icosahedral short-range order (ISRO) has been widely accepted to be dominant in Cu-Zr metallic glasses (MGs). However, the diffusion mechanism and correlation of ISRO and medium-range order (MRO) to diffusion in MGs remain largely unexplored. Here, we perform a long time annealing up to 1.8 μs in molecular dynamics simulations to study the diffusion mechanism and the relationship between atomic structures and the diffusion path in a Cu64.5Zr35.5 MG. It is found that most of the diffusing events performed by the diffusing atoms are outside ISRO and the Bergman-type MRO. The long-range diffusion in MGs is highly heterogeneous, via collective diffusing events through the liquidlike channels in the glass. Our results clearly demonstrate a strong correlation between the atomic structures and transport in MGs.
    Physical Review B 05/2015; 91(18). DOI:10.1103/PhysRevB.91.180201 · 3.74 Impact Factor
  • Min Wu · John S Tse · S.Y. Wang · C.Z. Wang · J.Z. Jiang ·
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    ABSTRACT: Phase transitions in amorphous alloys under pressure are an important fundamental problem. Here we report on a first-principles study that reproduces the recently discovered pressure-induced crystallization of amorphous Ce100-xAlx (x<25) alloys and reveals an atomistic transformation mechanism. Contrary to common belief, pressure-induced devitrification of an amorphous Ce-Al alloy is not due to the Ce 4f delocalization that is expected to bring the size of Ce atoms closer to that of Al atoms. Our theoretical results show that the Bader volume of Ce is always larger than that of Al. A continuous increase in the relative Ce/Al Bader volume leads to favourable conditions for forming a close-packed structure at high pressure. The results also show that the Hume-Rothery rules are not applicable to describe the structures of substitutional alloys at high pressure. This study provides a new perspective on the electron distribution in lanthanide alloys under the application of pressure.
    Nature Communications 03/2015; 6:6493. DOI:10.1038/ncomms7493 · 11.47 Impact Factor
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    ABSTRACT: We present an efficient genetic algorithm, integrated with experimental diffraction data, to solve a nanoscale metastable Al 20Sm4 phase that evolves during crystallization of an amorphous magnetron sputtered Al 90Sm10 alloy. The excellent match between calculated and experimental X-ray diffraction patterns confirms an accurate description of this metastable phase. Molecular dynamic simulations of crystal growth from the liquid phase predict the formation of disordered defects in the devitrified crystal.
    Applied Physics Letters 03/2015; 106(10):101903. DOI:10.1063/1.4914399 · 3.30 Impact Factor
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    G Q Yue · Y Zhang · Y Sun · B Shen · F Dong · Z Y Wang · R J Zhang · Y X Zheng · M J Kramer · S Y Wang · C Z Wang · K M Ho · L Y Chen ·
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    ABSTRACT: The short-range order (SRO) in Pd78Cu6Si16 liquid was studied by high energy x-ray diffraction and ab initio molecular dynamics (MD) simulations. The calculated pair correlation functions at different temperatures agree well with the experimental results. The partial pair correlation functions from ab intio MD simulations indicate that Si atoms prefer to be uniformly distributed while Cu atoms tend to aggregate. By performing structure analysis using Honeycutt-Andersen index, Voronoi tessellation, and atomic cluster alignment method, we show that the icosahedron and face-centered cubic SRO increase upon cooling. The dominant SRO is the Pd-centered Pd9Si2 motif, namely the structure of which motif is similar to the structure of Pd-centered clusters in the Pd9Si2 crystal. The study further confirms the existence of trigonal prism capped with three half-octahedra that is reported as a structural unit in Pd-based amorphous alloys. The majority of Cu-centered clusters are icosahedra, suggesting that the presence of Cu is benefit to promote the glass forming ability.
    Scientific Reports 02/2015; 5:8277. DOI:10.1038/srep08277 · 5.58 Impact Factor
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    Y. Zhang · F. Zhang · C. Z. Wang · M. I. Mendelev · M. J. Kramer · K. M. Ho ·
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    ABSTRACT: The atomic structure of metallic glasses (MGs) plays an important role in their properties. Numerous molecular dynamics (MD) simulations have revealed icosahedral short-range order (ISRO) as a dominant motif in Cu-Zr metallic glasses. However, the cooling rates utilized in most of the MD simulations (usually on the order of 1010–13K/s) can be too high to allow the structure to relax into the actual structures. By performing a long sub-Tg annealing of the Cu64.5Zr35.5 alloy model at 700 K up to 2.0μs using MD simulations, we systematically address the evolution of medium-range order (MRO) as the cooling rates in MD simulations approach the experimental cooling rates (usually 103–6K/s). By reducing the effective cooling rates to as low as 2.8×107K/s, we found a significant enhancement of the ISRO and Bergman-type MRO. Comparing to the widely used face-, edge-, or vertex-sharing icosahedra, we propose that the Bergman-type MRO is a much more unambiguous metric to characterize the MRO in Cu-Zr MGs. By analyzing the network formed by interpenetrating icosahedra using the graphical theory, we show that the degree of interpenetration of the icosahedra centers increases with decreasing cooling rates. The network becomes aggressively assortative, indicating that higher degree nodes tend to cluster and form backbones in the MG. All these results show that the networks in the models prepared using lower cooling rates strongly deviate from a stringlike morphology.
    Physical Review B 02/2015; 91(6). DOI:10.1103/PhysRevB.91.064105 · 3.74 Impact Factor
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    Z Y Wang · R J Zhang · S Y Wang · M Lu · X Chen · Y X Zheng · L Y Chen · Z Ye · C Z Wang · K M Ho ·
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    ABSTRACT: Nanostructure arrays such as nanowire, nanopillar, and nanocone arrays have been proposed to be promising antireflection structures for photovoltaic applications due to their great light trapping ability. In this paper, the optical properties of Si nanopillar and nanocone arrays in visible and infrared region were studied by both theoretical calculations and experiments. The results show that the Mie resonance can be continuously tuned across a wide range of wavelength by varying the diameter of the nanopillars. However, Si nanopillar array with uniform diameter exhibits only discrete resonance mode, thus can't achieve a high broadband absorption. On the other hand, the Mie resonance wavelength in a Si nanocone array can vary continuously as the diameters of the cross sections increase from the apex to the base. Therefore Si nanocone arrays can strongly interact with the incident light in the broadband spectrum and the absorbance by Si nanocone arrays is higher than 95% over the wavelength from 300 to 2000 nm. In addition to the Mie resonance, the broadband optical absorption of Si nanocone arrays is also affected by Wood-Rayleigh anomaly effect and metal impurities introduced in the fabrication process.
    Scientific Reports 01/2015; 5:7810. DOI:10.1038/srep07810 · 5.58 Impact Factor
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    ABSTRACT: Classically, the onset of nucleation is defined in terms of a critical cluster of the condensed phase, which forms from the gradual aggregation of randomly diffusing adatoms. Experiments in Pb/Si(111) at low temperature have discovered a dramatically different type of nucleation, with perfect crystalline islands emerging "explosively" out of the compressed wetting layer after a critical coverage Θ_{c}=1.22 ML is reached. The unexpectedly high island growth rates, the directional correlations in the growth of neighboring islands and the persistence in time of where mass is added in individual islands, suggest that nucleation is a result of the highly coherent motion of the wetting layer, over mesoscopic distances.
    Physical Review Letters 12/2014; 113(23):236101. DOI:10.1103/PhysRevLett.113.236101 · 7.51 Impact Factor
  • F. S. Ke · G. Q. Yue · B. Shen · F. Dong · S.Y. Wang · Y.X. Zheng · L.Y. Chen · C. Z. Wang · K. M. Ho ·
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    ABSTRACT: The structure of liquid and rapidly quenched amorphous Ag0.74Ge0.26 alloy at the eutectic composition was studied by ab initio molecular dynamics (MD) simulations. The local structural properties were systematically investigated from the liquid at 1123 K to amorphous solid at 300 K. The pair-correlation function at 976 K from the MD simulations agrees well with the experimental data. The local structures were also analyzed using Honeycutt-Andersen (HA) indices, Voronoi tessellation and the atomic cluster alignment (ACA) method. The HA indices analysis reveals that there is a high population of pentagonal bipyramid structure which become more predominant upon solidification. Voronoi tessellation analysis indicates strong icosahedral short-range order (SRO) in the liquid and amorphous samples generated by the MD simulations. Using the ACA method, the development of icosahedral SRO upon cooling is further confirmed and a Bergman medium-range order is also observed. The analysis of structural properties and chemical short-range order suggests that Ag atoms tend to have a Bergman-like packing, while the dispersed Ge atoms prevent the alloy from forming a long-range order upon cooling. The Bergman medium-range order is also confirmed by the constrained reversed Monte Carlo results.
    Acta Materialia 11/2014; 80:498-504. DOI:10.1016/j.actamat.2014.06.049 · 4.47 Impact Factor
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    ABSTRACT: Despite numerous studies on the atomic structures of Cu-Zr metallic glasses (MGs), their inherent structural ordering, e.g., medium-range order (MRO), remains difficult to describe. Specifically lacking is an understanding of how the MRO responds to deformation and the associated changes in atomic mobility. In this paper, we focus on the impact of deformation on MRO and associated effect on diffusion in a well-relaxed Cu64.5Zr35.5 MG by molecular dynamics simulations. The Cu-Zr MG exhibits a larger elastic limit of 0.035 and a yield stress of 3.5 GPa. The cluster alignment method was employed to characterize the icosahedral short-range order (ISRO) and Bergman-type medium-range order (BMRO) in the models upon loading and unloading. From this analysis, we find the disruption of both ISRO and BMRO occurs as the strain reaches about 0.02, well below the elastic limit. Within the elastic limit, the total fractions of ISRO or BMRO can be fully recovered upon unloading. The diffusivity increases six to eight times in regions undergoing plastic deformation, which is due to the dramatic disruption of the ISRO and BMRO. By mapping the spatial distributions of the mobile atoms, we demonstrate the increase in atomic mobility is due to the extended regions of disrupted ISRO and more importantly BMRO.
    Physical Review B 11/2014; 90(17). DOI:10.1103/PhysRevB.90.174101 · 3.74 Impact Factor
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    Y. Zhang · C. Z. Wang · F. Zhang · M. I. Mendelev · M. J. Kramer · K. M. Ho ·
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    ABSTRACT: Structural and dynamical heterogeneities in metallic glasses, while intensely studied, remain an enigma. For instance, whether and how the dynamical and structural heterogeneities are correlated is still an outstanding question. Meanwhile, the nature of the impact of medium-range order (MRO) on the dynamical heterogeneity remains elusive. In this paper, we analyzed the structural and dynamical heterogeneities in both as-quenched and relaxed Cu64.5Zr35.5 metallic glasses based on the atomistic trajectories collected from molecular dynamics simulations. We found that the majority of the mobile atoms are not involved in icosahedral clusters or Bergman superclusters, indicating that dynamical heterogeneities are strongly correlated with structural heterogeneities. The Bergman-type MRO has an even stronger correlation with the dynamical heterogeneity than the icosahedral short range order. Moreover, we found that the localized soft vibration modes below 1.0 THz are mostly concentrated on the mobile atoms. These results suggest that the vibrational properties can be conveniently utilized to predict the atomic mobility in metallic glasses, which can bridge the studies of dynamical heterogeneity by experiments and simulations. (C) 2014 AIP Publishing LLC.
    Applied Physics Letters 10/2014; 105(15). DOI:10.1063/1.4898779 · 3.30 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 10/2014; 611:167–170. DOI:10.1016/j.jallcom.2014.05.072 · 3.00 Impact Factor

Publication Stats

6k Citations
752.92 Total Impact Points


  • 2011-2015
    • U.S. Department of Energy
      • Ames Lab
      Washington, Washington, D.C., United States
  • 1989-2015
    • Iowa State University
      • • Ames Laboratory
      • • Department of Physics and Astronomy
      • • Department of Chemistry
      Ames, Iowa, United States
  • 2010
    • Qingdao University
      • College of Physics
      Tsingtao, Shandong Sheng, China
  • 2007
    • Jilin University
      • State Key Lab of Theoretical and Computational Chemistry
      Jilin, Jilin Sheng, China