693 research outputs found
Crystalline and Electronic Structures of Molecular Solid CCl: First-Principles Calculation
A molecular solid CCl 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
CCl are presented. The results show that CCl%
molecules can form either a hcp or fcc indirect-gap band insulator or an
insulating hexagonal monolayer.Comment: 5 pages, 6 figure
Half-Metallic Silicon Nanowires: Multiple Surface Dangling Bonds and Nonmagnetic Doping
By means of first-principles density functional theory calculations, we find
that hydrogen-passivated ultrathin silicon nanowires (SiNWs) along [100]
direction with symmetrical multiple surface dangling bonds (SDBs) and boron
doping can have a half-metallic ground state with 100% spin polarization, where
the half-metallicity is shown quite robust against external electric fields.
Under the circumstances with various SDBs, the H-passivated SiNWs can also be
ferromagnetic or antiferromagnetic semiconductors. The present study not only
offers a possible route to engineer half-metallic SiNWs without containing
magnetic atoms but also sheds light on manipulating spin-dependent properties
of nanowires through surface passivation.Comment: 4 pages, 5 figure
Thermal Conductance for Single Wall Carbon Nanotubes
We report a theoretical analysis of the phonon thermal conductance, \kappa
(T), for single wall carbon nanotubes (SWCN). In a range of low temperatues up
to 100K, \kappa (T) of perfect SWCN is found to increase with temperature,
approximately, in a parabolic fashion. This is qualitatively consistent with
recent experimental measurements where the tube-tube interactions are
negligibly weak. When the carbon-carbon bond length is slightly varied, \kappa
(T) is found to be qualitatively unaltered which implies that the anharmonic
effect does not change the qualitative behavior of \kappa (T).Comment: Revtex, 4 figure
Thermoelectric Properties of Silicon Carbide Nanowires with Nitrogen Dopants and Vacancies
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.Comment: 9 pages, 10 figure
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