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Search Results: 1 - 10 of 50412 matches for " Qing-Rong Zheng "
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Structures, Electronic Properties, Spectroscopies and Hexagonal Monolayer Phase of a Family of Unconventional Fullerenes C64X4 (X = H; F;Cl;Br)
Qing-Bo Yan,Qing-Rong Zheng,Gang Su
Physics , 2008,
Abstract: A systematic first-principles study within density functional theory on the geometrical structures and electronic properties of unconventional fullerene C64 and its derivatives C64X4 (X = H; F;Cl;Br) has been performed. By searching through all 3465 isomers of C64, the ground state of C64 is found to be spherical shape with D2 symmetry, which differs from the parent cage of the recently synthesized C64H4 that is pear-shaped with C3v symmetry. We found that the addition of the halogen atoms like F;Cl;Br to the pentagon-pentagon fusion vertex of C64 cage could enhance the stability, forming the unconventional fullerenes C64X4. The Mulliken charge populations, LUMO-HOMO gap energies and density of states are calculated, showing that different halogen atoms added to C64 will cause remarkably different charge populations of the C64X4 molecule; the chemical deriving could enlarge the energy gaps and affect the electronic structures distinctly. It is unveiled that C64F4 is even more stable than C64H4, as the C-X bond energy of the former is higher than that of the latter. The computed spectra of C64H4 molecules agree well with the experimental data; the IR, Raman, NMR spectra of C64X4 (X = F;Cl;Br) are also calculated to stimulate further experimental investigations. Finally, it is uncovered by total energy calculations that C64X4 could form a stable hexagonal monolayer.
Face-Centered-Cubic B$_{80}$ Metal: Density functional theory calculations
Qing-Bo Yan,Qing-Rong Zheng,Gang Su
Physics , 2008, DOI: 10.1103/PhysRevB.77.224106
Abstract: By means of ab initio calculations within the density functional theory, we have found that B80 fullerenes can condense to form stable face-centered-cubic fcc solids. It is shown that when forming a crystal, B80 cages are geometrically distorted, the Ih symmetry is lowered to Th, and four boron-boron chemical bonds are formed between every two nearest neighbor B80 cages. The cohesive energy of B80 fcc solid is 0.23 eV/atom with respect to the isolated B80 fullerene. The calculated electronic structure reveals that the fcc B80 solid is a metal. The predicted solid phase would constitute a form of pure boron and might have diverse implications. In addition, a simple electron counting rule is proposed, which could explain the stability of B80 fullerene and the recently predicted stable boron sheet.
Crystalline and Electronic Structures of Molecular Solid C$_{50}$Cl$% _{10}$: First-Principles Calculation
Qing-Bo Yan,Qing-Rong Zheng,Gang Su
Physics , 2005, DOI: 10.1103/PhysRevB.73.165417
Abstract: A molecular solid C$_{50}$Cl$_{10}$ with possible crystalline structures, including the hexagonal-close-packed (hcp) phase, the face-centered cubic (fcc) phase, and a hexagonal monolayer, is predicted in terms of first-principles calculation within the density functional theory. The stable structures are determined from the total-energy calculations, where the hcp phase is uncovered more stable than the fcc phase and the hexagonal monolayer in energy per molecule. The energy bands and density of states for hcp and fcc C$_{50}$Cl$_{10}$ are presented. The results show that C$_{50}$Cl% $_{10}$ molecules can form either a hcp or fcc indirect-gap band insulator or an insulating hexagonal monolayer.
trans-4-[(Phenylsulfonyloxy)methyl]cyclohexanecarboxylic acid
Yu-Feng Liang,Qing-Rong Qi,Hu Zheng
Acta Crystallographica Section E , 2008, DOI: 10.1107/s1600536808024513
Abstract: The title compound, C14H18O5S, is an important intermediate for the synthesis of poly(amidoamine) dendrimers. The cyclohexane ring adopts a chair conformation with its two substituents in equatorial positions. In the crystal structure, molecules form centrosymmetric dimers via O—H...O hydrogen bonds.
Xiao-Qiang Guo,Hu Zheng,Qing-Rong Qi
Acta Crystallographica Section E , 2011, DOI: 10.1107/s1600536811048392
Abstract: The asymmetric unit of the title compound, C12H16BrNO3S, contains two independent molecules. In each molecule, the azetidine four-membered ring adopts a nearly planar conformation, the maximum deviations being 0.087 (3) and 0.079 (3) . The mean azetidine plane is twisted by 75.2 (2) and 73.6 (2)° with respect to the plane of the benzene ring in the two independent molecules. The crystal packing is stabilized by O—H...O hydrogen bonds.
trans-4-(Tosyloxymethyl)cyclohexanecarboxylic acid
Qing-Rong Qi,Wen-Cai Huang,Hu Zheng
Acta Crystallographica Section E , 2008, DOI: 10.1107/s1600536807068572
Abstract: The title compound, C15H20O5S, is an intermediate in the synthesis of a new type of poly(amidoamine) (PAMAM) dendrimer. The cyclohexane ring exhibits a chair conformation, with C—C bond lengths in the range 1.518 (3)–1.531 (3) and C—C—C angles in the range 110.45 (19)–112.09 (19)°; these agree well with the values in other cyclohexane derivatives described in the literature. In the crystal structure, adjacent molecules are linked by O—H...·O hydrogen bonds. The H atoms of the methyl group are disordered equally over two positions.
Spin transfer in a ferromagnet-quantum dot and tunnel barrier coupled Aharonov-Bohm ring system with Rashba spin-orbit interactions
Xi Chen,Qing-Rong Zheng,Gang Su
Physics , 2010, DOI: 10.1088/0953-8984/22/18/186004
Abstract: The spin transfer effect in ferromagnet-quantum dot (insulator)-ferromagnet Aharonov-Bohm (AB) ring system with Rashba spin-orbit (SO) interactions is investigated by means of Keldysh nonequilibrium Green function method. It is found that both the magnitude and direction of the spin transfer torque (STT) acting on the right ferromagnet electrode can be effectively controlled by changing the magnetic flux threading the AB ring or the gate voltage on the quantum dot. The STT can be greatly augmented by matching a proper magnetic flux and an SO interaction at a cost of low electrical current. The STT, electrical current, and spin current are uncovered to oscillate with the magnetic flux. The present results are expected to be useful for information storage in nanospintronics.
Classical and Quantum Chaotic Behaviors of Two Colliding Harmonic Oscillators
Qing-Rong Zheng,Gang Su,De-Hai Zhang
Physics , 1995, DOI: 10.1016/0375-9601(96)00003-5
Abstract: We have systematically studied both classical and quantum chaotic behaviors of two colliding harmonic oscillators. The classical case falls in Kolmogorov-Arnold-Moser class. It is shown that there exists an energy threshold, above which the system becomes nonintegrable. For some values of the initial energy near the threshold, we have found that the ratio of frequencies of the two oscillators affects the Poincar\'e sections significantly. The largest Lyapunov character exponent depends linearly on the ratio of frequencies of the two oscillators away from the energy threshold in some chaotic regions, which shows that the chaotic behaviors of the system are mainly determined by the ratio. In the quantum case, for certain parameters, the distribution of the energy level spacings also varies with the ratio of frequencies of the two oscillators. The relation between the energy spectra and the ratio of frequencies of the two oscillators, the interaction constant, and the semi-classical quantization constant, is also investigated respectively.
Quantum Oscillations of Tunnel Magnetoresistance Induced by Spin-Wave Excitations in Ferromagnet-Ferromagnet-Ferromagnet Double Barrier Tunnel Junctions
Xi Chen,Qing-Rong Zheng,Gang Su
Physics , 2008, DOI: 10.1103/PhysRevB.76.144409
Abstract: The possibility of quantum oscillations of the tunnel conductance and magnetoresistance induced by spin-wave excitations in a ferromagnet-ferromagnet-ferromagnet double barrier tunnel junction, when the magnetizations of the two side ferromagnets are aligned antiparallel to that of the middle ferromagnet, is investigated in a self-consistent manner by means of Keldysh nonequilibrium Green function method. It has been found that owing to the s-d exchange interactions between conduction electrons and the spin density induced by spin accumulation in the middle ferromagnet, the differential conductance and the TMR indeed oscillate with the increase of bias voltage, being consistent with the phenomenon that is observed recently in experiments. The effects of magnon modes, the energy levels of electrons as well as the molecular field in the central ferromagnet on the oscillatory transport property of the system are also discussed.
Thermoelectric Properties of Silicon Carbide Nanowires with Nitrogen Dopants and Vacancies
Zhuo Xu,Qing-Rong Zheng,Gang Su
Physics , 2012, DOI: 10.1103/PhysRevB.84.245451
Abstract: The thermoelectric properties of cubic zincblend silicon carbide nanowires (SiCNWs) with nitrogen impurities and vacancies along [111] direction are theoretically studied by means of atomistic simulations. It is found that the thermoelectric figure of merit ZT of SiCNWs can be significantly enhanced by doping N impurities together with making Si vacancies. Aiming at obtaining a large ZT, we study possible energetically stable configurations, and disclose that, when N dopants locate at the center, a small number of Si vacancies at corners are most favored for n-type nanowires, while a large number of Si vacancies spreading into the flat edge sites are most favored for p-type nanowires. For the SiCNW with a diameter of 1.1 nm and a length of 4.6 nm, the ZT value for the n-type is shown capable of reaching 1.78 at 900K. The conditions to get higher ZT values for longer SiCNWs are also addressed.
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