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ABSTRACT: We demonstrate an interesting phase transition from cold compressed benzene to a fully saturated three-dimensional hydrocarbon crystal, Hex-CH. The very low transition point pressure, remarkable energetic stability and positive dynamical stability indicate that Hex-CH is a promising three-dimensional hydrocarbon crystal. As a transparent insulator and potential hard hydrocarbon material, Hex-CH is expected to be of general interest in organic chemistry, condensed matter physics and material science.
Journal of Physics Condensed Matter 04/2013; 25(20):205403. · 2.55 Impact Factor
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ABSTRACT: Systematic enumeration of crystalline networks with some special topological
characters is of considerable interest in both mathematics and crystallography.
Based on the restriction of lattice in cubic and inequivalent nodes not
exceeding three, a simple method is proposed for systematic searching for
three-dimensional crystalline networks with only sp2-configuration nodes
(C-sp2-TDTCNs). We systematically scan the cubic space groups from No.195 to
No.230 and find many C-sp2-TDTCNs including all the previously proposed cubic
ones. These C-sp2-TDTCNs are topologically intriguing and can be considered as
good templates for searching carbon crystals with novel properties, predicting
high pressure phases of element nitrogen and designing three-dimensional
hydrocarbon crystals. Structure optimizations are considered by regrading these
C-sp2-TDTCNs as carbon crystals and the corresponding energetic stability of
these carbon crystals are evaluated, using the the density functional theory
(DFT) based first-principle calculations. Our results are of wide interests in
mathematics, condensed physics, crystallography and material science.
02/2013;
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ABSTRACT: The electronic and magnetic properties of single 3d transition-metal(TM) atom
(V, Cr, Mn, Fe, Co, and Ni) adsorbed graphdiyne (GDY) and graphyne (GY) are
systematically studied using first-principles calculations within the density
functional framework. We find that the adsorption of TM atom not only
efficiently modulates the electronic structures of GDY/GY system, but also
introduces excellent magnetic properties, such as half-metal and spin-select
half-semiconductor. Such modulation originates from the charge transfer between
TM adatom and the GDY/GY sheet as well as the electron redistribution of the TM
intra-atomic s, p, and d orbitals. Our results indicate that the TM adsorbed
GDY/GY are excellent candidates for spintronics.
07/2012;
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ABSTRACT: Using first-principles method within the framework of the density functional
theory, we study the influence of native point defect on the structural and
electronic properties of Bi$_2$Se$_3$. Se vacancy in Bi$_2$Se$_3$ is a double
donor, and Bi vacancy is a triple acceptor. Se antisite (Se$_{Bi}$) is always
an active donor in the system because its donor level ($\varepsilon$(+1/0))
enters into the conduction band. Interestingly, Bi antisite(Bi$_{Se1}$) in
Bi$_2$Se$_3$ is an amphoteric dopant, acting as a donor when
$\mu$$_e$$<$0.119eV (the material is typical p-type) and as an acceptor when
$\mu$$_e$$>$0.251eV (the material is typical n-type). The formation energies
under different growth environments (such as Bi-rich or Se-rich) indicate that
under Se-rich condition, Se$_{Bi}$ is the most stable native defect independent
of electron chemical potential $\mu$$_e$. Under Bi-rich condition, Se vacancy
is the most stable native defect except for under the growth window as
$\mu$$_e$$>$0.262eV (the material is typical n-type) and
$\Delta$$\mu$$_{Se}$$<$-0.459eV(Bi-rich), under such growth windows one
negative charged Bi$_{Se1}$ is the most stable one.
06/2012;
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ABSTRACT: Using first-principles method, we investigate the energetic stability,
dynamic stability and electronic properties of two three-dimensional (3D)
all-sp2 carbon allotropes, sp2-diamond and cubic-graphite. The cubic-graphite
was predicted by Michael O'Keeffe in 1992 (Phys. Rev. Lett., 68, 15, 1992.)
possessing space group of Pn-3m (224), whereas the sp2-diamond with the space
group Fd-3m (227) same as that of diamond has not been reported before. Our
results indicate that sp2-diamond is more stable than previously proposed
K4-carbon and T-carbon, and cubic-graphite is even more stable than superhard
M-carbon, W-carbon and Z-carbon.The calculations on vibrational properties show
that both structures are dynamically stable. Interestingly, both sp2-diamond
and cubic-graphite behave as semiconductors which are contrary to previously
proposed all-sp2 carbon allotropes. The sp2-diamond is a semiconductor with a
direct band gap of 1.66 eV, and cubic-graphite is an indirect semiconductor
with band gap of 2.89 eV. The very lower densities and entirely sp2 configures
of sp2-diamond and cubic-graphite can be potentially applied in
hydrogen-storage, photocatalysts and molecular sieves.
06/2012;
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ABSTRACT: We propose a new allotrope of graphane, named as tricycle graphane,with a
4up/2down UUUDUD hydrogenation in each hexagonal carbon ring,which is different
from previously proposed allotropes with UUDUUD(boat-1) and UUUUDD (boat-2)
types of hydrogenation. Its stability and electronic structures are
systematically studied using first-principles method. We find that the tricycle
graphane is a stable phase in between the previously proposed chair and stirrup
allotropes. Its electronic properties are very similar to those of chair,
stirrup, boat-1, boat-2, and twist-boat allotropes. The negative Gibbs free
energy of tricycle graphane is -91 meV/atom, which very close to that of the
most stable chair one (-103 meV/atom). Thus, this new two-dimensional
hydrocarbon may be produced in the process of graphene hydrogenation with a
relative high probability compared to other conformers.
04/2012;
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ABSTRACT: A superhard boron nitride phase dubbed as Z-BN is proposed as possible
intermediate phase between h-BN and zinc blende BN (c-BN), and investigated
using first-principles calculations within the framework of the density
functional theory. Although the structure of Z-BN is similar to that of bct-BN
containing four-eight BN rings, it is more energy favorable than bct-BN. Our
study reveals that Z-BN, with a considerable structural stability and high
density comparable to c-BN, is a transparent insulator with an indirect band
gap about 5.27 eV. Amazingly, its Vickers hardness is 55.88 Gpa which is
comparable to that of c-BN. This new BN phase may be produced in experiments
through cold compressing AB stacking h-BN due to its low transition pressure
point of 3.3 GPa.
04/2012;
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ABSTRACT: Using a generalized genetic algorithm, we propose four new sp3 carbon
allotropes with 5-6-7 (5-6-7-type Z-ACA and Z-CACB) or 4-6-8(4-6-8-type Z4-A3B1
and A4-A2B2) carbon rings. Their stability, mechanical and electronic
properties are systematically studied using first-principles method. We find
that all these four carbon allotropes show amazing stability in comparison with
recently proposed carbon phases. Both ZACA and Z-CACB are direct-band-gap
semiconductors with band gaps of 2.261 eV and 4.196 eV, respectively. Whereas
Z4-A3B1 and A4-A2B2 are indirect-band-gap semiconductors with band gaps of
3.105 eV and 3.271 eV, respectively. Their mechanical properties reveal that
all these four carbon allotropes are superhard materials comparable to diamond.
03/2012;
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ABSTRACT: Two new carbon allotropes (H-carbon and S-carbon) are proposed, as possible
candidates for the intermediate superhard phases between graphite and diamond
obtained in the process of cold compressing graphite, based on the results of
first-principles calculations. Both H-carbon and S-carbon are more stable than
previously proposed M-carbon and W-carbon and their bulk modulus are comparable
to that of diamond. H-carbon is an indirect-band-gap semiconductor with a gap
of 4.459 eV and S-carbon is a direct-band-gap semiconductor with a gap of 4.343
eV. The transition pressure from cold compressing graphite is 10.08 GPa and
5.93 Gpa for H-carbon and S-carbon, respectively, which is in consistent with
the recent experimental report.
03/2012;
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ABSTRACT: The transport properties of zigzag graphene nanoribbons (ZGNRs) decorated by carboxyl group (OH) chains are systematically investigated using the density functional theory in combination with the nonequilibrium Green’s function method. ZGNRs with nine zigzag carbon chains (9ZGNR) decorated by mOH (m is the number of oxidized carbon chains) are taken as typical systems. We find that the OH chains can effectively modulate the electronic structures and transport properties of the 9ZGNR. The systems behave as metal when m ≤ 4, and a transmission plateau up to 6G0 is found around the Fermi level when m = 3. However, when m > 4, the 9ZGNR-mOH systems become semiconductors. Interestingly, 9ZGNR-7OH and 9ZGNR-8OH behave as n-type semiconductors. It is found that such modulation depends on the edge states as well as the oxygen atoms at the interface. When the width of undecorated carbon regions is <3, Peierls instability induces the metal–semiconductor transition.
10/2011;
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ABSTRACT: The transport properties of hybrid nanoribbons formed by partially substituting zigzag boron nitride (graphene) nanoribbons into zigzag graphene (boron nitride) nanoribbons are investigated using the first-principles nonequilibrium Green’s function method. The transport properties are highly improved with the transmission conductance around the Fermi level increasing to 3G0 in hybrid systems based on zigzag graphene nanoribbons and to 2G0 in hybrid systems based on zigzag boron nitride nanoribbons. The enhancement is attributed to the coupling effect between B (N) atoms and C atoms at the interface of hybrid systems, which introduces a pair of bonding and antibonding bands around the Fermi level. The transport enhancement also remains in hybrid nanoribbons sandwiched into gold electrodes. The currents of such devices are improved compared with those of pristine ones, which originate from the additional transport channels at the C–B interface.
05/2011;
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ABSTRACT: Electronic structures and optical properties of hexagonal boron nitride (h-BN) under hydrostatic pressure are studied using density functional theory calculations. Charge density difference, density of states, band structures, and dielectric functions are calculated to reveal the evolution of the electronic structures, band-gap, and optical properties of five typical stackings of h-BN corresponding to the hydrostatic pressures. The band-gap of h-BN decreases with the increasing hydrostatic pressure. The band-gap of h-BN with AA and AF stacking decreases faster than that of the others. The positions of their valence band maximum and the conduction band minimum shift in the Brillouin Zone corresponding to the external hydrostatic pressure, depending on the different stackings. In particular, the band structure of AA becomes direct at 9.19 GPa, which does not occur in other stackings. The band-edge optical absorption thresholds of AA, AD, AE, and AF show the redshift as the pressure increases, except for that of AB stacking, which is fluctuant.
Journal of Applied Physics 04/2011; 109(7):073708-073708-7. · 2.17 Impact Factor
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ABSTRACT: The transport properties of the devices made by corrugated graphene nanoribbons were investigated using the density functional theory in combination with the nonequilibrium Green’s function method. We find that the transport properties of the zigzag graphene nanoribbons (ZGNRs) with arched corrugation are similar to the flat one, while the transmission of the ZGNRs with step-shaped corrugation is greatly depressed. As for the armchair graphene nanoribbons (AGNRs), arched corrugation enlarges the transmission gap and the threshold voltage of the device. Moreover, the open currents of AGNRs are significantly depressed by both stepped and arched corrugation.
Applied Physics Letters 04/2010; 96(17):173101-173101-3. · 3.84 Impact Factor
