243 research outputs found
New structural model for GeO2/Ge interface: A first-principles study
First-principles modeling of a GeO2/Ge(001) interface reveals that sixfold
GeO2, which is derived from cristobalite and is different from rutile,
dramatically reduces the lattice mismatch at the interface and is much more
stable than the conventional fourfold interface. Since the grain boundary
between fourfold and sixfold GeO2 is unstable, the sixfold GeO2 forms a large
grain at the interface. On the contrary, a comparative study with SiO2
demonstrates that SiO2 maintains a fourfold structure. The sixfold GeO2/Ge
interface is shown to be a consequence of the ground-state phase of GeO2. In
addition, the electronic structure calculation reveals that sixfold GeO2 at the
interface shifts the valence band maximum far from the interface toward the
conduction band.Comment: 18 pages, 5 figures, and 2 table
First-Principles Study on Electron-Conduction Properties of C Chains
The electron-conduction properties of fullerene chains are examined by
first-principles calculations based on the density functional theory. The
conductivity of the C dimer is low owing to the constraint of the
junction of the molecules on electron conduction, whereas the C monomer
exhibits a conductance of 1 G. One of the three degenerate
states of C is relevant to conduction and the contributions of the
others are small. In addition, we found a more interesting result that the
conductance of the fullerene chain is drastically increased by encapsuling
metal atoms into cages.Comment: 10pages and 5 figure
Magnetic orderings in Al nanowires suspended between electrodes
A theoretical analysis of a relation between atomic and spin-electronic
structures for the ground state of single-row aluminum nanowires suspended
between Al(001) electrodes is demonstrated using first-principles
molecular-dynamics simulations. We obtain a unusual result that a
3-aluminum-atom nanowire sandwiched between the electrodes does not manifest
magnetic ordering although an isolated aluminum trimer molecule in a straight
line is spin-polarized. On the other hand, a 5-atom nanowire exhibits
ferromagnetic ordering, where three central atoms form a spin-polarized trimer.
Moreover, in the case of an 8-atom nanowire, the middle atoms in the nanowire
form two spin-polarized trimers with antiferromagnetic ordering.Comment: 9 page
Improvement of accuracy of wave-function-matching method for transport calculation
The wave-function-matching (WFM) technique for first-principles
transport-property calculations was modified by S\o{}rensen {\it et al.} so as
to exclude rapidly decreasing evanescent waves [S\o{}rensen {\it et al.}, Phys.
Rev. B {\bf 77}, 155301 (2008)]. However, this method lacks translational
invariance of the transmission probability with respect to insertion of
matching planes and consistency between the sum of the transmission and
reflection probabilities and the number of channels in the transition region.
We reformulate the WFM method since the original methods are formulated to
include all the generalized Bloch waves. It is found that the translational
invariance is destroyed by the overlap of the layers between the electrode and
transition regions and by the pseudoinverses used to exclude the rapidly
decreasing evanescent waves. We then devise a method that removes the overlap
and calculates the transmission probability without the pseudoinverses. As a
result, we find that the translational invariance of the transmission
probability with respect to insertion of the extra layers is properly retained
and the sum of the transmission and reflection probabilities exactly agrees
with the number of channels. In addition, we prove that the accuracy in the
transmission probability of this WFM technique is comparable with that obtained
by the nonequilibrium Green's function method. Furthermore, we carry out the
electron transport calculations on two-dimensional graphene sheets embedded
with B--N line defects sandwiched between a pair of semi-infinite graphene
electrodes and find the dependence of the electron transmission on the
transverse momentum perpendicular to the direction of transport
New structural model for GeO2/Ge interface: A first-principles study
First-principles modeling of a GeO2/Ge(001) interface reveals that sixfold
GeO2, which is derived from cristobalite and is different from rutile,
dramatically reduces the lattice mismatch at the interface and is much more
stable than the conventional fourfold interface. Since the grain boundary
between fourfold and sixfold GeO2 is unstable, the sixfold GeO2 forms a large
grain at the interface. On the contrary, a comparative study with SiO2
demonstrates that SiO2 maintains a fourfold structure. The sixfold GeO2/Ge
interface is shown to be a consequence of the ground-state phase of GeO2. In
addition, the electronic structure calculation reveals that sixfold GeO2 at the
interface shifts the valence band maximum far from the interface toward the
conduction band.Comment: 18 pages, 5 figures, and 2 table
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