The Experts below are selected from a list of 11295 Experts worldwide ranked by ideXlab platform
A. R. Oganov - One of the best experts on this subject based on the ideXlab platform.
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phagraphene a low energy graphene Allotrope composed of 5 6 7 carbon rings with distorted dirac cones
Nano Letters, 2015Co-Authors: Zhenhai Wang, Q. Zhu, Xiangfeng Zhou, Xiaoming Zhang, Huafeng Dong, Mingwen Zhao, A. R. OganovAbstract:Using systematic evolutionary structure searching we propose a new carbon Allotrope, phagraphene (fae'graefi:n), standing for penta-hexa-hepta-graphene, because the structure is composed of 5-6-7 carbon rings. This two-dimensional (2D) carbon structure is lower in energy than most of the predicted 2D carbon Allotropes due to its sp 2 -binding features and density of atomic packing comparable to graphene. More interestingly, the electronic structure of phagraphene has distorted Dirac cones. The direction-dependent cones are further proved to be robust against external strain with tunable Fermi velocities.
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Novel sp^3 forms of carbon predicted by evolutionary metadynamics and analysis of their synthesizability using transition path sampling
Journal of Superhard Materials, 2012Co-Authors: S. E. Boulfelfel, Q. Zhu, A. R. OganovAbstract:Experiments on cold compression of graphite have indicated the existence of a new superhard and transparent Allotrope of carbon. Numerous metastable candidate structures featuring different topologies have been proposed for “superhard graphite”, showing a good agreement with experimental X-ray data. In order to determine the nature of this new Allotrope, we use evolutionary metadynamics to systematically search for low-enthalpy sp^3 carbon structures easily accessible from graphite and we employ molecular-dynamics transition path sampling to investigate the corresponding kinetic pathways starting from graphite at 15–20 GPa. Real transformation kinetics are computed and physically meaningful transition mechanisms are produced at the atomistic level of detail in order to demonstrate how nucleation mechanism and transformation kinetics lead to M-carbon as final product of cold compression of graphite. This establishes M-carbon as an experimentally synthesized carbon Allotrope.
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Systematic search for low-enthalpy sp3 carbon Allotropes using evolutionary metadynamics
Physical Review B, 2012Co-Authors: Q. Zhu, Qingfeng Zeng, A. R. OganovAbstract:We present a systematic search for low-energy metastable superhard carbon Allotropes by using the recently developed evolutionary metadynamics technique. It is known that cold compression of graphite produces an Allotrope at 15–20 GPa. Here we look for all low-enthalpy structures accessible from graphite. Starting from 2Hor 3R-graphite and applying a pressure of 20 GPa, a large variety of intermediate sp 3 carbon Allotropes were observed in evolutionary metadynamics simulation. Our calculation not only found all the previous proposed candidates for “superhard graphite,” but also predicted two Allotropes (X-carbon and Y -carbon) showing unusual types of 5 + 7a nd 4+ 8 topologies. These superhard carbon Allotropes can be classified into five families based on 6 (diamond/lonsdaleite), 5 + 7( M -a ndW-carbon), 5 + 7( X-carbon), 4 + 8 (bct-C4), and 4 + 8( Y -carbon) topologies. This study shows that evolutionary metadynamics is a powerful approach both to find the global minima and systematically search for low-energy metastable phases reachable from given starting materials.
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Denser than diamond: Ab initio search for superdense carbon Allotropes
Physical Review B, 2011Co-Authors: Q. Zhu, A. R. Oganov, Miguel A. Salvadó, Pilar Pertierra, Andriy O. LyakhovAbstract:A). Searching for possible superdense carbon Allotropes, we have found three structures (hP3, tI12, and tP12) that have significantly greater density. The hP3 and tP12 phases have strong analogy with two polymorphs of silica (β-quartz and keatite), while the tI12 phase is related to the high-pressure SiS2 polymorph. Furthermore, we found a collection of other superdense structures based on the motifs of the aforementioned structures, but with different ways of packing carbon tetrahedra, and among these the hP3 and tI12 structures are the densest. At ambient conditions, the hP3 phase is a semiconductor with the GW band gap of 3.0 eV, tI12 is an insulator with the band gap of 5.5 eV, while tP12 is an insulator, the band gap of which is remarkably high (7.3 eV), making it the widest-gap carbon Allotrope. These Allotropes are metastable and have comparable to diamond or slightly higher bulk moduli; their Vickers hardnesses are calculated to be 87.6 GPa for hP3, 87.2 GPa for tI12, and 88.3 GPa for tP12, respectively, thus making these Allotropes nearly as hard as diamond (for which the same model gives the hardness of 94.3 GPa). Superdense carbon Allotropes are predicted to have remarkably high refractive indices and strong dispersion of light.
Yu Jia - One of the best experts on this subject based on the ideXlab platform.
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c 57 carbon a two dimensional metallic carbon Allotrope with pentagonal and heptagonal rings
Computational Materials Science, 2019Co-Authors: Chun-xiang Zhao, Chun-yao Niu, Jiaqi Wang, Yu Jia, Yiqi YangAbstract:Abstract By means of the first-principles calculations, we have theoretically investigated the structural stability and electronic properties of a two-dimensional planar metallic carbon Allotrope named C-57 carbon which possesses the P 6 ¯ 2 m ( D 3 h 3 ) symmetry. This carbon Allotrope is an all- sp 2 hybridized bonding network consisting of 5–7 rings of carbon atoms. The stability of C-57 carbon is confirmed through phonon-mode analysis, total energy and elastic constants calculations, as well as first-principles molecular dynamics simulations. We conceived that the metallicity of C-57 carbon is attributed to the large states across Fermi-level contributed by p y orbital due to the bond distortion, which is much different from that of graphite. This new carbon sheet can also serve as a precursor for stable one-dimensional nanotubes with metallic character. These results broaden our understanding of two-dimensional carbon Allotropes and will attract more researchers to focus the research on the field of two-dimensional carbon materials. Besides, the C-57 carbon may be useful for designing of nano-electronic devices.
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c 20 t carbon a novel superhard sp 3 carbon Allotrope with large cavities
Journal of Physics: Condensed Matter, 2016Co-Authors: Jiaqi Wang, Chun-xiang Zhao, Chun-yao Niu, Qiang Sun, Yu JiaAbstract:Through first-principles calculations, we predict a new superhard carbon Allotrope named C 20 - T, which possesses a cubic T symmetry with space group No.198(P213). This new carbon Allotrope has an all-sp (3) hybridized bonding network with 20 atoms in its primitive unit cell. The dynamic, mechanical, and thermal stabilities of this new carbon phase at zero pressure are confirmed by using a variety of state-of-the-art theoretical calculations. Interestingly, despite the fact that C 20 - T carbon has a porous structure with large cavities, our calculations identify its superhard properties with the Vickers hardness of 72.76 Gpa. The ideal tensile and shear strength of C 20 - T carbon are calculated to be 71.1 and 55.2 GPa respectively, comparable to that of c-BN. Electronic band calculations reveal that this new carbon Allotrope is a transparent insulator with an indirect band gap of 5.44 eV. These results broaden our understanding of superhard carbon Allotropes.
Q. Zhu - One of the best experts on this subject based on the ideXlab platform.
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phagraphene a low energy graphene Allotrope composed of 5 6 7 carbon rings with distorted dirac cones
Nano Letters, 2015Co-Authors: Zhenhai Wang, Q. Zhu, Xiangfeng Zhou, Xiaoming Zhang, Huafeng Dong, Mingwen Zhao, A. R. OganovAbstract:Using systematic evolutionary structure searching we propose a new carbon Allotrope, phagraphene (fae'graefi:n), standing for penta-hexa-hepta-graphene, because the structure is composed of 5-6-7 carbon rings. This two-dimensional (2D) carbon structure is lower in energy than most of the predicted 2D carbon Allotropes due to its sp 2 -binding features and density of atomic packing comparable to graphene. More interestingly, the electronic structure of phagraphene has distorted Dirac cones. The direction-dependent cones are further proved to be robust against external strain with tunable Fermi velocities.
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Novel sp^3 forms of carbon predicted by evolutionary metadynamics and analysis of their synthesizability using transition path sampling
Journal of Superhard Materials, 2012Co-Authors: S. E. Boulfelfel, Q. Zhu, A. R. OganovAbstract:Experiments on cold compression of graphite have indicated the existence of a new superhard and transparent Allotrope of carbon. Numerous metastable candidate structures featuring different topologies have been proposed for “superhard graphite”, showing a good agreement with experimental X-ray data. In order to determine the nature of this new Allotrope, we use evolutionary metadynamics to systematically search for low-enthalpy sp^3 carbon structures easily accessible from graphite and we employ molecular-dynamics transition path sampling to investigate the corresponding kinetic pathways starting from graphite at 15–20 GPa. Real transformation kinetics are computed and physically meaningful transition mechanisms are produced at the atomistic level of detail in order to demonstrate how nucleation mechanism and transformation kinetics lead to M-carbon as final product of cold compression of graphite. This establishes M-carbon as an experimentally synthesized carbon Allotrope.
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Systematic search for low-enthalpy sp3 carbon Allotropes using evolutionary metadynamics
Physical Review B, 2012Co-Authors: Q. Zhu, Qingfeng Zeng, A. R. OganovAbstract:We present a systematic search for low-energy metastable superhard carbon Allotropes by using the recently developed evolutionary metadynamics technique. It is known that cold compression of graphite produces an Allotrope at 15–20 GPa. Here we look for all low-enthalpy structures accessible from graphite. Starting from 2Hor 3R-graphite and applying a pressure of 20 GPa, a large variety of intermediate sp 3 carbon Allotropes were observed in evolutionary metadynamics simulation. Our calculation not only found all the previous proposed candidates for “superhard graphite,” but also predicted two Allotropes (X-carbon and Y -carbon) showing unusual types of 5 + 7a nd 4+ 8 topologies. These superhard carbon Allotropes can be classified into five families based on 6 (diamond/lonsdaleite), 5 + 7( M -a ndW-carbon), 5 + 7( X-carbon), 4 + 8 (bct-C4), and 4 + 8( Y -carbon) topologies. This study shows that evolutionary metadynamics is a powerful approach both to find the global minima and systematically search for low-energy metastable phases reachable from given starting materials.
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Denser than diamond: Ab initio search for superdense carbon Allotropes
Physical Review B, 2011Co-Authors: Q. Zhu, A. R. Oganov, Miguel A. Salvadó, Pilar Pertierra, Andriy O. LyakhovAbstract:A). Searching for possible superdense carbon Allotropes, we have found three structures (hP3, tI12, and tP12) that have significantly greater density. The hP3 and tP12 phases have strong analogy with two polymorphs of silica (β-quartz and keatite), while the tI12 phase is related to the high-pressure SiS2 polymorph. Furthermore, we found a collection of other superdense structures based on the motifs of the aforementioned structures, but with different ways of packing carbon tetrahedra, and among these the hP3 and tI12 structures are the densest. At ambient conditions, the hP3 phase is a semiconductor with the GW band gap of 3.0 eV, tI12 is an insulator with the band gap of 5.5 eV, while tP12 is an insulator, the band gap of which is remarkably high (7.3 eV), making it the widest-gap carbon Allotrope. These Allotropes are metastable and have comparable to diamond or slightly higher bulk moduli; their Vickers hardnesses are calculated to be 87.6 GPa for hP3, 87.2 GPa for tI12, and 88.3 GPa for tP12, respectively, thus making these Allotropes nearly as hard as diamond (for which the same model gives the hardness of 94.3 GPa). Superdense carbon Allotropes are predicted to have remarkably high refractive indices and strong dispersion of light.
Shengbai Zhang - One of the best experts on this subject based on the ideXlab platform.
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A low-surface energy carbon Allotrope: the case for bcc-C6
arXiv: Materials Science, 2016Co-Authors: Wen-jin Yin, Yuanping Chen, Yuee Xie, Li-min Liu, Shengbai ZhangAbstract:Graphite may be viewed as a low-surface-energy carbon Allotrope with little layer-layer interaction. Other low-surface-energy Allotropes but with much stronger layer-layer interaction may also exist. Here, we report a first-principles prediction for one of the known carbon Allotropes, bcc-C6 (a body centered carbon Allotrope with six atoms per primitive unit) that should have exceptionally low-surface energy and little size dependence down to only a couple layer thickness. This unique property may explain the existence of the relatively-high-energy bcc-C6 during growth. The electronic properties of the bcc-C6thin layers can also be intriguing: the (111), (110), and (001) thin layers havedirect band gap, indirect band gap, and metallic character, respectively. The refrained chemical reactivity of the thin layers does not disappear after cleaving, as lithium-doped (Li-doped) 3-layers (111) has a noticeably increased binding energies of H2 molecules with a maximum storage capacity of 10.8 wt%.
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A low-surface energy carbon Allotrope: the case for bcc-C6
Physical chemistry chemical physics : PCCP, 2015Co-Authors: Wen-jin Yin, Yuanping Chen, Yuee Xie, Li-min Liu, Shengbai ZhangAbstract:Graphite may be viewed as a low-surface-energy carbon Allotrope with little layer–layer interaction. Other low-surface-energy Allotropes but with much stronger layer–layer interaction may also exist. Here, we report a first-principles prediction for one of the known carbon Allotropes, bcc-C6 (a body centered carbon Allotrope with six atoms per primitive unit), that should have exceptionally low-surface energy and little size dependence down to only a couple layer thickness. This unique property may explain the existence of the relatively-high-energy bcc-C6 during growth. The electronic properties of the bcc-C6 thin layers can also be intriguing: the (111), (110), and (001) thin layers have direct band gap, indirect band gap, and metallic character, respectively. The refrained chemical reactivity of the thin layers does not disappear after cleaving, as lithium-doped (Li-doped) 3-layers (111) has a noticeably increased binding energy of H2 molecules with a maximum storage capacity of 10.8 wt%.
Yoshiyuki Kawazoe - One of the best experts on this subject based on the ideXlab platform.
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topological nodal line semimetal in an orthorhombic graphene network structure
Physical Review B, 2018Co-Authors: Jiantao Wang, Changfeng Chen, Yoshiyuki KawazoeAbstract:Topological semimetals are a fascinating class of quantum materials that possess extraordinary electronic and transport properties. These materials have attracted great interest in recent years for their fundamental significance and potential device applications. Currently a major focus in this research field is to theoretically explore and predict and experimentally verify and realize material systems that exhibit a rich variety of topological semimetallic behavior, which would allow a comprehensive characterization of the intriguing properties and a full understanding of the underlying mechanisms. In this paper, we report on ab initio calculations that identify a carbon Allotrope with simple orthorhombic crystal structure in $Pbcm$ (${D}_{2h}^{11}$) symmetry. This carbon Allotrope can be constructed by inserting zigzag carbon chains between the graphene layers in graphite or by a crystalline modification of a (3,3) carbon nanotube with a double cell reconstruction mechanism. Its dynamical stability has been confirmed by phonon and molecular dynamics simulations. Electronic band calculations indicate that it is a nodal-line semimetal comprising two nodal lines that go through the whole Brillouin zone in bulk and a projected surface flat band around the Fermi level. The present findings establish an additional topological semimetal system in the nanostructured carbon Allotropes family and offer insights into its outstanding structural and electronic properties.