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Now showing items 1 - 16 of 26

  • Electronic structure and magnetism of ThFeAsN

    Guangtao Wang   Xianbiao Shi  

    The electronic structure and magnetic properties of ThFeAsN, a newly discovered superconductor, are investigated by means of first-principles calculations. ThFeAsN shares electronic structure and magnetic properties similar to those of LaOFeAs. Its calculated ground state is the stripe antiferromagnetic state. The hole-like Fermi surfaces (FSs) along the line largely overlap with the electron-like FS along the line with the vector . Such significant FS nesting induces a peak of the bare susceptibility at the M-point.
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  • A new classification algorithm recommendation method based on link prediction

    Xiaoyan Zhu   Xiaomei Yang   Chenzhen Ying   Guangtao Wang  

    Abstract Recommending appropriate classification algorithm(s) for a given classification problem is of great significance and also one of the challenging problems in the field of data mining, which is usually viewed as a meta-learning problem. Multi-label learning has been adopted and validated to be an effective meta-learning method in classification algorithm recommendation. However, the multi-label learning method used in previous classification algorithm recommendation relies only on relationship between data sets and their direct neighbours, ignoring the impact of other data sets. In this paper, a new classification algorithm recommendation method based on link prediction between data sets and classification algorithms is proposed. Taking advantage of link prediction in heterogeneous networks, this method considers the impact of all data sets and makes full use of the interactions between data sets as well as between data sets and algorithms. Firstly, meta data of the training data sets is collected. And then a heterogeneous network called DAR ( D ata and A lgorithm R elationship) Network is constructed with the meta data. Finally, the link prediction technique is adopted to recommend appropriate algorithm(s) for a given data set on the basis of the DAR Network . To evaluate the proposed link prediction-based recommendation method, extensive experiments with 131 data sets and 21 classification algorithms are conducted. Results of 5 performance measures indicate that the proposed method is more effective compared with the base line classification algorithm recommendation method and can be used in practice.
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  • Topological phase transition in half-Heusler compounds HfIrX (X = As, Sb, Bi)

    Guangtao Wang   JunHong Wei  

    Graphical abstract Highlights • We find topological insulator and Weyl-semimetal in HfIrX (X = As, Sb, Bi). • We control the topological phases transition by the pressure and atoms substitution. • We explained the physical reasons of the topological phases transition. Abstract We studied the lattice constant and atoms substitution tunable topological phase transition in the half-Heusler compounds HfIrX (X = As, Sb, Bi). At the equilibrium cubic crystal structure and excluding SOC, HfIrAs and HfIrBi are topological nontrivial semimetal, while HfIrSb is a trivial topological insulator. This is because that the “internal pressure” lifts the s-type Γ 1 band above p-type Γ 5 bands in HfIrSb. When SOC is included, HfIrAs and HfIrSb become topological insulator, and normal band insulator, respectively, while HfIrBi is still a topological semimetal. When we induce compressive stress in the ab-plane of HfIrBi, it becomes a Weyl semimetal, with eight Weyl-Points (WPS) at ( ± K x , 0, ± K z ), (0, ± K y , ± K z ), K x = K y = 0.023 Å −1 , K z = 0.108 Å −1 .
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  • The Orbital Ordering of the Cubic Kcrf 3

    Minping Zhang   Guangtao Wang  

    The electronic, magnetic and orbital structures of KCrF 3 in the cubic phase are studied by first principles method. In the cubic phase, the three Cr-F bonds distance are equal. If the Jahn-Teller distortion is the origin of the orbital polarization, the orbital ordering would disappear. However, our theoretical calculations show that the orbital ordering exists even without the Jahn-Teller distortion. By studying how the orbital polarization changes with the electron correlation and the Jahn-Teller distortion, we found that the origin of the orbital polarization should be the electron correlation and the Jahn-Teller distortion can reinforced such polarization.
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  • Comparative study of the magnetism of SrTcO3 and Ca(Sr)MnO3

    Guangtao Wang   Lei Li   Chang Liu   Minping Zhang   Zongxian Yang  

    By the first-principles calculations, we studied the electronic structures and the magnetic properties of SrTcO3 and Ca(Sr)MnO3. We found the strikingly high Néel temperature of SrTcO3 is mostly due to the strong Tc(4d)-O(2p) hybridizations, since the Tc-4d states are more extended than the Mn-3d states. Such Tc(4d)-O(2p) hybridizations increase the super-exchange constants, hence increased the Néel temperatures.
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  • The electronic structure of ScVO3

    Guangtao Wang   Jubao Yang   Chang Liu   Minping Zhang  

    The electronic, magnetic and orbital structures of ScVO 3 are studied by first-principles calculations. The local density approximation (LDA) results show that the ground state is ferromagnetic (FM) state, with a moment of 1.70 muB on V 3+ ion. While LDA+U results indicate that the ground state is G-type spin order (G-SO), with a moment of 1.75 muB on V 3+, which agrees with experiment results. The two electrons of V 3+ occupy the d zx and d zy orbitals. The spin order and orbital order structures of ScVO 3 are different from those of LaVO 3 (C-SO, and G-OO) and YVO 3 (G-SO, and C-OO) due to the different Jahn-Teller distortions. [All rights reserved Elsevier].
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  • Comparative study of the magnetism of SrTcO3 and Ca(Sr)MnO3

    Guangtao Wang   Lei Li   Chang Liu   Minping Zhang   Zongxian Yang  

    By the first-principles calculations, we studied the electronic structures and the magnetic properties of SrTcO3 and Ca(Sr)MnO3. We found the strikingly high Néel temperature of SrTcO3 is mostly due to the strong Tc(4d)-O(2p) hybridizations, since the Tc-4d states are more extended than the Mn-3d states. Such Tc(4d)-O(2p) hybridizations increase the super-exchange constants, hence increased the Néel temperatures.
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  • The electronic structure and magnetism of KxFe2Se2

    Guangtao Wang   Minping Zhang   Lihua Zheng   Zongxian Yang  

    Within the virtual crystal approximation and model, the electronic structures and magnetic properties of iron-selenide () are studied by first-principles calculations. Its phase diagram can be classified into two different phases: (I) the collinear antiferromagnetic state (), and (II) the bi-collinear antiferromagnetic state (). Such magnetic phases can be well explained by the competition among the nearest, next-nearest, and next-next-nearest neighbor couplings , , and .
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  • The electronic structure and magnetism of KxFe2Se2

    Guangtao Wang   Minping Zhang   Lihua Zheng   Zongxian Yang  

    Within the virtual crystal approximation and model, the electronic structures and magnetic properties of iron-selenide () are studied by first-principles calculations. Its phase diagram can be classified into two different phases: (I) the collinear antiferromagnetic state (), and (II) the bi-collinear antiferromagnetic state (). Such magnetic phases can be well explained by the competition among the nearest, next-nearest, and next-next-nearest neighbor couplings , , and .
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  • Selecting feature subset for high dimensional data via the propositional FOIL rules

    Guangtao Wang   Qinbao Song   Baowen Xu   Yuming Zhou  

    Feature interaction is an important issue in feature subset selection. However, most of the existing algorithms only focus on dealing with irrelevant and redundant features. In this paper, a propositional FOIL rule based algorithm FRFS, which not only retains relevant features and excludes irrelevant and redundant ones but also considers feature interaction, is proposed for selecting feature subset for high dimensional data. FRFS first merges the features appeared in the antecedents of all FOIL rules, achieving a candidate feature subset which excludes redundant features and reserves interactive ones. Then, it identifies and removes irrelevant features by evaluating features in the candidate feature subset with a new metric CoverRatio, and obtains the final feature subset. The efficiency and effectiveness of FRFS are extensively tested upon both synthetic and real world data sets, and it is compared with other six representative feature subset selection algorithms, including CFS, FCBF, Consistency, Relief-F, INTERACT, and the rule-based FSBAR, in terms of the number of selected features, runtime and the classification accuracies of the four well-known classifiers including Naive Bayes, C4.5, PART and IB1 before and after feature selection. The results on the five synthetic data sets show that FRFS can effectively identify irrelevant and redundant features while reserving interactive ones. The results on the 35 real world high dimensional data sets demonstrate that compared with other six feature selection algorithms, FRFS cannot only efficiently reduce the feature space, but also can significantly improve the performance of the four well-known classifiers. [All rights reserved Elsevier].
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  • Orbital ordering in Mott-insulators La2O3Fe2Se2 and La2O3Co2Se2

    Guangtao Wang   Minping Zhang   Lihua Zheng   Zongxian Yang  

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  • The first-principles studying LaOMnSe: A possible parent compound of superconductor

    Guangtao Wang   Lihua Zheng   Minping Zhang   Zongxian Yang  

    By the first-principles calculations, we studied the structure, electronic and magnetic properties of LaOMnSe. The band structure and Fermi surface of LaOMnSe are very similar to those of LaOFeAs, where there are three hole-like Fermi surfaces around Gamma-point and two electron-like Fermi surfaces around M-point. The hole-like Fermi surfaces will strongly overlap with electron-like Fermi surfaces if they are shifted by the q vector (pi, pi, 0). Such Fermi surfaces nesting will induce magnetic instability and spin density wave (SDW), which is similar to LaOFeAs. Because of so much similarity to LaOFeAs, LaOMnSe is expected to become superconductor with electron or hole doping. [All rights reserved Elsevier].
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  • The electronic structure and magnetism of a new layered iron selenide superconductor: LiOHFeSe

    Guangtao Wang   Xia Yi   Xianbiao Shi  

    Highlights • Study the electronic and magnetic properties of LiOHFeSe. • Find the Fermi surfaces nesting induced spin density wave. • Explain the superconductivity in Li 0.8 Fe 0.2 OHFeSe, and predict the superconductivity in Li 1 − x OHFeSe. Abstract We studied the electronic structure and magnetic properties of LiOHFeSe with first-principle calculations. The strong Fermi-surface nesting in the nonmagnetic state induces magnetic instability and the spin-density-wave state, which is more stable than the other states. The calculated bare susceptibility χ 0 ( q ) peaked at the M-point and it was obviously suppressed with increasing electron and hole doping.
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  • Potential parent compound of superconductor: Sr2CuM2As2O2 (M = Mn, Fe)

    Guangtao Wang   Minping Zhang   Lihua Zheng   Zongxian Yang  

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  • The electronic structure and magnetism of CaFeAs<sub>2</sub>: First principles calculations

    Guangtao Wang   Xianbiao Shi   Lin Zhang   Xia Yi  

    Abstract The electronic structure, magnetism and Fermi surface (FS) nesting of the recently discovered superconductive parent material CaFeAs 2 are studied by the first-principles, based on the GGA and GGA+U methods. In the nonmagnetic state, the density of states at the Fermi level are mostly derived from the dxy , dyz and dzx orbits, just like LaOFeAs. The Fermi surfaces consist of four hole like FS sheets around the Γ -point, two electron like sheets near the Brillouin zone corner M-point, and small pockets near X-point. The hole like Fermi surfaces will strongly overlap with the electron like FS sheets, if they are shifted by the q-vector q=( π , π , 0). Such FS nesting will induce the magnetic instability and spin density wave (SDW), which has been confirmed to be more stable than other states by the calculated total energy. The calculated bare susceptibility χ 0 (q) peaked at M-point, and was obviously suppressed with the electron doping. This explains the emergence of the superconductivity in the electron-doped compound Ca 1 − x Lax FeAs 2 , because the electron doping suppressed the SDW and induced the superconductivity. Highlights • We studied the electronic structure and magnetism of CaFeAs 2 . • Studied the Fermi surface nesting at different electron and hole-doping. • We calculated the bare susceptibility and found it is different with LaOFeAs.
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  • Geochemical evidence for seasonal variations in potential loess sources of the western Chinese Loess Plateau

    Xunming Wang   Lili Lang   Hui Li   Ting Hua   Guangtao Wang   Na Zhou   Linlin Jiao  

    Abstract This paper aims to characterize seasonal variations in the potential sources of loess deposited on the western Chinese Loess Plateau (CLP). Fallout was sampled every five days between March 2013 and August 2014 at Jiuzhoutai, the site with the largest loess deposits in northwest China. A total of 45 macro and trace elements, as well as rare earth elements, were analyzed in the samples. The results show that, at present, the potential sources of loess are mixed with pollutants. After exclusion of the pollutants, principal component analysis (PCA) showed significant seasonal variations in the potential loess sources on the western CLP. During the spring, summer–autumn, and winter periods, there are possibly six, four, and two potential loess sources, respectively, with crustal provenance at Jiuzhoutai. No significant differences in fallout amounts were found on the western CLP during periods with and without dust events, which suggests that the frequency of dust events may not be an effective index for deposition rates in areas of loess formation. The relatively high proportion of coarser material (>50 μm in diameter) in the fallout indicates that at least part of the loess in the fallout samples originated from adjacent deserts and associated systems, and that both dry and wet deposition contributed equally to the fallout. Based on the significant seasonal and spatial variations in the loess sources, combined with variations in the link between the different particle size classes and the geochemical characteristics of potential components of the loess on the western CLP, the use of the geochemical characteristics of loess stratigraphic sequences as a proxy for regional paleoclimatic and environmental reconstructions should be carefully appraised. Highlights • Source of the loess deposited on the western Chinese Loess Plateau (CLP) varies. • Dust-event frequency may not be an effective index for loess deposition rates. • The link between particle size and geochemistry of loess source areas is complex. • Both dry and wet deposition are equally important on the western CLP. • Using loess-sequence geochemistry as a regional climate proxy should be appraised.
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