Cai Zhuang Wang
Iowa State University
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Featured researches published by Cai Zhuang Wang.
Journal of Chemical Physics | 2004
W. C. Lu; Cai Zhuang Wang; Michael W. Schmidt; Laimutis Bytautas; K. M. Ho; Klaus Ruedenberg
A method is presented for expressing the occupied self-consistent-field (SCF) orbitals of a molecule exactly in terms of chemically deformed atomic minimal-basis-set orbitals that deviate as little as possible from free-atom SCF minimal-basis orbitals. The molecular orbitals referred to are the exact SCF orbitals, the free-atom orbitals referred to are the exact atomic SCF orbitals, and the formulation of the deformed quasiatomic minimal-basis-sets is independent of the calculational atomic orbital basis used. The resulting resolution of molecular orbitals in terms of quasiatomic minimal basis set orbitals is therefore intrinsic to the exact molecular wave functions. The deformations are analyzed in terms of interatomic contributions. The Mulliken population analysis is formulated in terms of the quasiatomic minimal-basis orbitals. In the virtual SCF orbital space the method leads to a quantitative ab initio formulation of the qualitative model of virtual valence orbitals, which are useful for calculating electron correlation and the interpretation of reactions. The method is applicable to Kohn-Sham density functional theory orbitals and is easily generalized to valence MCSCF orbitals.
Physical Review B | 2011
Min Ji; Koichiro Umemoto; Cai Zhuang Wang; Kai-Ming Ho; Renata M. Wentzcovitch
We propose three new phases of H2O under ultrahigh pressure. Our structural search was performed using an adaptive genetic algorithm which allows an extensive exploration of crystal structure. The new sequence of pressure-induced transitions beyond ice X at 0 K should be ice X! Pbcm ! Pbca ! Pmc21 ! P21 ! P21=c phases. Across the Pmc21-P21 transition, the coordination number of oxygen increases from 4 to 5 with a significant increase of density. All stable crystalline phases have nonmetallic band structures up to 7 TPa.
Journal of Chemical Physics | 2004
W. C. Lu; Cai Zhuang Wang; Michael W. Schmidt; Laimutis Bytautas; K. M. Ho; Klaus Ruedenberg
The method, introduced in the preceding paper, for recasting molecular self-consistent field (SCF) or density functional theory (DFT) orbitals in terms of intrinsic minimal bases of quasiatomic orbitals, which differ only little from the optimal free-atom minimal-basis orbitals, is used to elucidate the bonding in several silicon clusters. The applications show that the quasiatomic orbitals deviate from the minimal-basis SCF orbitals of the free atoms by only very small deformations and that the latter arise mainly from bonded neighbor atoms. The Mulliken population analysis in terms of the quasiatomic minimal-basis orbitals leads to a quantum mechanical interpretation of small-ring strain in terms of antibonding encroachments of localized molecular-orbitals and identifies the origin of the bond-stretch isomerization in Si4H6. In the virtual SCF/DFT orbital space, the method places the qualitative notion of virtual valence orbitals on a firm basis and provides an unambiguous ab initio identification of the frontier orbitals.
Proteins | 2005
W. C. Lu; Cai Zhuang Wang; Edward W. Yu; Kai-Ming Ho
The Escherichia coli AcrB multidrug transporter recognizes a wide range of toxic chemicals and actively extrudes them from cells. The molecular basis of multidrug transport in AcrB remains unknown. Herein, we describe normal mode analyses to study important regions for drug recognition and extrusion in this transporter. Based on the X‐ray structure of AcrB, an elastic network model has been able to correct errors arising from crystal imperfection in the experimental B‐factors. The results allow us to understand the functional dynamics of this membrane protein. It is expected that this technique can be applied to other membrane proteins with known structures. Proteins 2006.
Scientific Reports | 2015
Xin Zhao; Shunqing Wu; Xiaobao Lv; Manh Cuong Nguyen; Cai Zhuang Wang; Zijing Lin; Zi-Zhong Zhu; Kai-Ming Ho
Using a motif-network search scheme, we studied the tetrahedral structures of the dilithium/disodium transition metal orthosilicates A2MSiO4 with Au2009=u2009Li or Na and Mu2009=u2009Mn, Fe or Co. In addition to finding all previously reported structures, we discovered many other different tetrahedral-network-based crystal structures which are highly degenerate in energy. These structures can be classified into structures with 1D, 2D and 3D M-Si-O frameworks. A clear trend of the structural preference in different systems was revealed and possible indicators that affect the structure stabilities were introduced. For the case of Na systems which have been much less investigated in the literature relative to the Li systems, we predicted their ground state structures and found evidence for the existence of new structural motifs.
Journal of Physical Chemistry Letters | 2017
Yongliang Shi; Huijuan Sun; Wissam A. Saidi; Manh Cuong Nguyen; Cai Zhuang Wang; Kai-Ming Ho; Jinlong Yang; Jin Zhao
In contrast with theoretical predictions in which anatase TiO2(001) and its (1 × 4) reconstructed surfaces are highly reactive, recent experimental results show this surface to be inert except for the defect sites. In this report, based on a systematic study of anatase TiO2(001)-(1 × 4) surface using first-principles calculations, the tensile stress is shown to play a crucial role on the surface reactivity. The predicted high reactivity based on add-molecule model is due to the large surface tensile stress, which can be easily suppressed by a stress-release mechanism. We show that various surface defects can induce stress release concomitantly with surface passivation. Thus the synthesis of anatase(001) surface with few defects is essential to improve the reactivity, which can be achieved, for example, via H2O adsorption. Our study provides a uniform interpretation of controversial experimental observations and theoretical predictions on anatase TiO2(001) surface and further proposes new insights into the origin of surface reactivity.
Physical Review Letters | 2016
Valentin Taufour; Udhara S. Kaluarachchi; Rustem Khasanov; Manh Cuong Nguyen; Z. Guguchia; P. K. Biswas; P. Bonfà; Roberto De Renzi; Xiao Lin; Stella K. Kim; Eundeok Mun; Hyunsoo Kim; Yuji Furukawa; Cai Zhuang Wang; Kai-Ming Ho; Sergey L. Bud’ko; Paul C. Canfield
The temperature-pressure phase diagram of the ferromagnet LaCrGe_{3} is determined for the first time from a combination of magnetization, muon-spin-rotation, and electrical resistivity measurements. The ferromagnetic phase is suppressed near 2.1xa0GPa, but quantum criticality is avoided by the appearance of a magnetic phase, likely modulated, AFM_{Q}. Our density functional theory total energy calculations suggest a near degeneracy of antiferromagnetic states with small magnetic wave vectors Q allowing for the potential of an ordering wave vector evolving from Q=0 to finite Q, as expected from the most recent theories on ferromagnetic quantum criticality. Our findings show that LaCrGe_{3} is a very simple example to study this scenario of avoided ferromagnetic quantum criticality and will inspire further study on this material and other itinerant ferromagnets.
Physical Review B | 2016
Xin Zhao; Cai Zhuang Wang; Yongxin Yao; Kai-Ming Ho
Structures and magnetic properties of Fe16–xCoxN2 are studied using adaptive genetic algorithm and first-principles calculations. We show that substituting Fe with Co in Fe16N2 with a Co/Fe ratio ≤1 can greatly improve the magnetic anisotropy of the material. The magnetocrystalline anisotropy energy from first-principles calculations reaches 3.18 MJ/m3 (245.6 μeV per metal atom) for Fe12Co4N2, much larger than that of Fe16N2, and is one of the largest among the reported rare-earth-free magnets. From our systematic crystal structure searches, we show that there is a structure transition from tetragonal Fe16N2 to cubic Co16N2 in Fe16–xCoxN2 as the Co concentration increases, which can be well explained by electron counting analysis. As a result, different magnetic properties between the Fe-rich (x ≤ 8) and Co-rich (x > 8) Fe16–xCoxN2 is closely related to the structural transition.
Journal of Applied Physics | 2015
Xin Zhao; Liqin Ke; Manh Cuong Nguyen; Cai Zhuang Wang; Kai-Ming Ho
The structures and magnetic properties of the Co-Zr-B alloys near the Co5Zr composition were studied using adaptive genetic algorithm and first-principles calculations to guide further experimental effort on optimizing their magnetic performances. Through extensive structural searches, we constructed the contour maps of the energetics and magnetic moments of the Co-Zr-B magnet alloys as a function of composition. We found that the Co-Zr-B system exhibits the same structural motif as the Co11Zr2 polymorphs, which plays a key role in achieving high coercivity. Boron atoms can either substitute selective cobalt atoms or occupy the interstitial sites. First-principles calculation shows that the magnetocrystalline anisotropy energies can be significantly improved through proper boron doping.
Journal of Physics D | 2016
Jie Zhang; Manh Cuong Nguyen; Balamurugan Balasubramanian; Bhaskar Das; David J. Sellmyer; Zhi Zeng; Kai-Ming Ho; Cai Zhuang Wang
The structure and magnetic properties of new magnetic Fe3Co3 X 2 (X = Ti, Nb) compounds are studied by genetic algorithm, first-principles density functional theory (DFT) calculations, and experiments. The atomic structure of a hexagonal structure with P-6m2 symmetry is determined. The simulated x-ray diffraction (XRD) spectra of the P-6m2 structures agree well with experimental XRD data for both Fe3Co3Ti2 and Fe3Co3Nb2. The magnetic properties of these structures as well as the effect of the disorder of Fe and Co on their magnetic properties are also investigated. The magnetocrystalline anisotropy energy is found to be very sensitive to the occupancy disorder between Fe and Co.