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161.
We investigate the strain effects on the electronic properties of boron nitride nanoribbons (BNNFts) by using firstprinciples calculations. The results show that the energy gap of BNNRs with both armchair edges (A-BNNRs) and zigzag edges (Z-BNNFts) decreases as the strain increases. As strain increases, the energy gaps of Z-BNNRs decrease rapidly as the width increases and reduce significantly to small values, which makes Z-BNNRs change from wide-gap to narrow-gap semiconductors. 相似文献
162.
V. Srivastava M. Rajagopalan S. P. Sanyal 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(2):131-139
A first-principles tight-binding linear muffin tin orbital (TB-LMTO) method
within the local-density approximation is used to calculate the total
energy, lattice parameter, bulk modulus, magnetic moment, density of states
and energy band structures of half-metallic CrO2 at ambient as well as
at high pressure. The magnetic and structural stabilities are determined
from the total energy calculations. From the present study we predict a
magnetic transition from ferromagnetic (FM) state to a non-magnetic (NM)
state at 65 GPa, which is of second order in nature. We also observe from
our calculations that CrO2 is more stable in tetragonal phase
(rutile-type) at ambient conditions and undergoes a transition to an
orthorhombic structure (CaCl2-type) at 9.6 GPa, which is in good
agreement with the experimental results. We predict a second structural
phase transition from CaCl2- to fluorite-type structure at 89.6 GPa
with a volume collapse of 7.3%, which is yet to be confirmed
experimentally. Interestingly, CrO2 shows half metallicity under
ambient conditions. After the first structural phase transition from
tetragonal to orthorhombic, half metallicity has been retained in CrO2 and it vanishes at a pressure of 41.6 GPa. Ferromagnetism is quenched at a
pressure of 65 GPa. 相似文献
163.
Parameters of the electric quadrupole interaction for the first excited state (E=89.7 keV) of 99Ru nuclei for a number of the cubic Laves phase compounds Ce1−xLaxRu2, synthesized at high pressure, were determined by the perturbed angular γγ-correlation method. Compounds were synthesized at 8 GPa. It was revealed that the decrease of the average valence of a rare earth ion, caused by the substitution of La for Ce, results in the monotonous decrease of the quadrupole frequency νQ from 43.3 MHz for CeRu2 to 33.1 MHz for LaRu2. 相似文献
164.
The structural stability of CeAg has been studied by self-consistent full-potential linearized augmented plane wave method (FP_LAPW) based on the density functional theory (DFT). The result shows that the low-temperature phase of CeAg is not a simple tetragonal structure. The degenerate d states at the Fermi level are split because of atomic shifts, which result in the cubic-to-tetragonal transition. 相似文献
165.
Measurements of electrical resistivity are presented for polycrystalline alloys in the CePt2(Si1−xSnx)2 system. Results of X-ray diffraction indicate that the tetragonal region of the CePt2(Si1−xSnx)2 alloy system that is amenable for study only extends up to x=0.3. The resistivity maximum characteristic of a Kondo lattice is observed at a temperature Tmax=63 K for the parent compound CePt2Si2 and shifts to lower temperatures with increase in Sn content. The compressible Kondo lattice model is applied to describe the results of Tmax in terms of the on-site Kondo exchange interaction J and the electron density of states at the Fermi level N(EF). A value of |JN(EF)|=0.060±0.009 for the parent compound is obtained from the experimental results. 相似文献
166.
In this paper we present a first-principle study on the energetics of a single As2 molecule on GaSb(0 0 1) reconstructed surface. In order to shed light into the mechanisms of anion exchange at the Sb-rich GaSb(0 0 1) surface, we studied firstly As2 adsorption and then As for Sb exchange. We identify a surface region where both the processes are energetically favored. The results of this twofold analysis can be combined to derive possible reaction paths for the anion exchange process. 相似文献
167.
C. Wang C. Y. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):243-247
An ideal single vacancy can be formed by removing one carbon atom
from a hexagonal network. The vacancy is one of the most important
defect structures in carbon nanotubes (CNTs). Vacancies can
affect the mechanical, chemical, and electronic properties of CNTs.
We have systematically investigated single vacancies and their
related point defects for achiral, single-walled carbon nanotubes
(SWNTs) using first-principles calculations. The structures around
single vacancies undergo reconstruction without constraint, forming ground-stateor metastable-state structures. The 5-1DB
and 3DB point defects can be
formed in armchair CNTS, while the 5-1DB-P and 5-1DB-T point defects can be
formed in zigzag CNTs. The related point defects can transform into
each other under certain conditions. The formation energies of
armchair CNTs change smoothly with the tube radius, while in the
case of the 3DB defect, as the radius get larger, the formation energies
tend towards a constant value. 相似文献
168.
We have performed relativistic first-principles full-potential linearized augmented plane wave (FLAPW) calculation for rare earth palladium sulfide EuPd3S4 in the ferromagnetic and antiferromagnetic states. The density of 4f electrons of Eu is taken from a local-spin-density approximation self-interaction correction (LSDA-SIC) atomic calculation. EuPd3S4 is found to exhibit antiferromagnetic ordering in its ground state. The charge, orbital, magnetic moment and spin ordering are explained with the electronic structure, the orbital-projected density of states and the total energy study. EuPd3S4 is found to be stable in the body-centered Type-I antiferromagnetic state, in agreement with experimental results. Different Eu states are found in antiferromagnetic ordering. The magnetic moments of different states obtained through spin-polarized calculation are also in good agreement with experimental results. The phenomena observed are explained by the orbital hybridization of Eu and Pd ions as compared with the free ions. 相似文献
169.
Wilson Agerico Diño Yoshio Miura Hiroshi Nakanishi Tsuyoshi Sugimoto 《Solid State Communications》2004,132(10):713-718
We investigate and discuss how hydrogen behaves at the edges of a graphite sheet, in particular the armchair edge. Our density functional theory-based calculations results show that, in contrast to the zigzag edge [W.A. Diño, H. Nakanishi, H. Kasai, T. Sugimoto, T. Kondoe, e-J. Surf. Sci. Nanotech. 2 (2004) 77. [25]], regardless of orientation, there is an activation barrier hindering H2 dissociation at the armchair edges. And once they do get dissociatively adsorbed at the armchair edges, we find that it would be extremely hard to desorb the H from their adsorption sites at the armchair edges. Furthermore, we also found that, consistent with our earlier conclusions [W.A. Diño, Y. Miura, H. Nakanishi, H. Kasai, T. Sugimoto, J. Phys. Soc. Jpn. 72 (2003) 1867. [24]], it is unlikely that we would find a whole H2 in between plain graphite sheets. 相似文献
170.
The hydrogen absorption properties of CeMnGe, CeFeSi and CeCoX (X=Si and Ge) have been investigated. Neutron powder diffraction performed on deuteride CeCoGeD indicates that D-atoms are inserted in the pseudo-tetrahedral interstices [Ce4] of the tetragonal CeFeSi-type structure of this compound. Magnetization and electrical resistivity measurements reveal that the hydrogenation of: (i) CeCoSi and CeCoGe leads to the transition antiferromagnet→spin fluctuation behaviour; (ii) CeMnGe suppress the magnetic ordering of the Ce-moments. These results which suggest a lost of ordered magnetic moment on the Ce site after hydrogenation could result from the chemical effect of hydrogen which prevails over the unit cell expansion effect. 相似文献