共查询到20条相似文献,搜索用时 515 毫秒
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S. P. Gabuda S. G. Kozlova S. B. Érenburg N. V. Bausk R. L. Davidovich V. V. Zyryanov Yu. M. Yukhin 《JETP Letters》2002,76(1):50-52
The results of XANES spectroscopy and DFT calculations are evidence for the occurrence of anomalous 2p2/3→6s1/2 electronic transitions in lead(II) and bismuth(III) oxides. The observed transitions may be due to the tunneling of outer 6s2 electrons. 相似文献
3.
Band structure of hydrides has been studied by density functional calculations. From analysis of band structures, it is found that, similar to semiconductors, some hydrides possess open fundamental band gap, and can be classified according to the following three characteristic features. The first is based on the value of the fundamental band gap and, therefore, the hydrides have been classified as narrow or wide band gap materials. The second feature is based on a comparison of the relative location in k space of the bottommost conduction band and topmost valence band (VB). Thus, hydrides can be classified as either direct or indirect band gap materials. The third feature is based on the origin of the topmost valence band and depends on the dominant contribution of s-, p-, and d-electrons to the topmost VB. According to this criterion, hydrides can be classified as type s, p, d or hybridised materials. This classification will be useful in the application of hydrides for the construction and processing of electronic devices within the framework of the recent innovations in ‘hydride electronics’. 相似文献
4.
M. V. Krasin’kova 《Technical Physics》2002,47(5):543-549
A model of chemical bonds in manganates that allows for one-electron covalent σ bonding between manganese and oxygen ions is suggested. One-electron covalent bonding results in the strongly correlated state of electrons due to exchange interaction between the electrons when they are shared by the cation and anion orbitals. The correlated state shows up as the spatial ordering of electrons and the ordering of their spins, causing the spin-ordered electron lattice to form. In this model, electrical conduction in manganates takes place when the electron lattice (more precisely, its part) shifts from one site of localization to another. The conductivity of the material depends on the type of the spin order of electrons in the electron lattice and on the energy of localization, which is defined by the energy of one-electron σ bonding. The model also implies the strong cationic polarization of anions, which facilitates the 3s2p hybridization of anions and the transition of one of the pairs of 2p electrons from the singlet state to the triplet one. The 3s2p hybridization of anions favors the formation of the spin-polarized electron lattice (the electron spins are parallel) and the ferromagnetic ordering of manganese ions. Under these assumptions, the effect of giant magnetoresistance is explained by a change in the conduction mechanism when an external voltage is applied. In this case, the conduction mechanism typical of ionic crystals changes to that specified by the spin-polarized electron lattice. 相似文献
5.
K. Mageshwari R. Sathyamoorthy P. Sudhagar Yong Soo Kang 《Applied Surface Science》2011,257(16):7245-7253
Nanostructured bismuth sulfide thin films were prepared onto glass substrates with particle size of 21 nm by thermal evaporation using readily prepared bismuth sulfide nanocrystallite powder. The X-ray diffraction pattern revealed that bismuth sulfide thin films exhibit orthorhombic structure. The existence of quantum confinement effect was confirmed from the observed band gap energy of 1.86 eV. AC and DC electrical conductivity of Al/BiSnc/Al structures was investigated in the frequency range 0.5-100 kHz at different temperatures (303-463 K) under vacuum. The AC conductivity (σac) is found to be proportional to angular frequency (ωs). The obtained experimental result of the AC conductivity showed that the correlated barrier hopping model is the appropriate mechanism for the electron transport in the nanostructured bismuth sulfide thin films. DC conduction mechanism in these films was studied and possible conduction mechanism in the bismuth sulfide thin films was discussed. 相似文献
6.
Self-consistent cellular multiple scattering techniques and photoemission energy distribution curves obtained at 20<hv<80 eV are used to study the density of states of UN and US. The calculations are based on a model using a finite cluster of atoms in a condensed-matter-like boundary potential. The main results refer to the mixing of thes, p, d, andf-states of uranium into a valence and a conduction band. Thef-states form orbitals with the ligands, within the valence and conduction bands. In the nitride the amount off character in the valence band is only 0.3 electrons and thef electrons are in two resonant levels (of each spin) in the conduction band. Only the first of these levels is occupied for the local, alternate from atom to atom, majority spin. In the sulfide the amount off character in the valence band is 0.59 electrons and the rest of thef-levels are in a resonance state (of majority spin) at the beginning of the conduction band. The conduction band is mainly of localized uranium 6d character. The theoretical results compare favorably with the photoemission data reported here. 相似文献
7.
J. Andriessen 《Molecular physics》2013,111(6):1103-1113
In the restricted Hartree-Fock scheme approximate SCF-LCAO calculations have been performed for the [Mn(H2O)]6 2+ complex using a minimal basis set consisting of nine Slater-type orbitals of the manganese ion and four Slater-type orbitals of the water molecule. The 1s, 2s and 2p orbitals of the manganese ion and the 1s orbital of the oxygen atom are treated as frozen core orbitals. In evaluating the different parts of the Hartree-Fock operators we used a two-centre approximation for the multicentre integrals. A new aspect of the calculations is the use of the Hartree-Fock orbital energies of the free water molecule as a first approximation for the corresponding orbital energies of the complex. The calculations have been done for the ground states and six excited states of the complex with symmetry T h and also for the ground states of two distorted complexes. From the resulting eigenvectors we calculated the hyperfine interaction of the valence electrons of the central ion with the protons of the water molecules for three different geometries. The excited states give two different ways of finding values of 10 Dq and the Racah parameters B and C. The results are encouraging. 相似文献
8.
J. A. McLeod A. V. Lukoyanov E. Z. Kurmaev L. D. Finkelstein A. Moewes 《JETP Letters》2011,94(2):142-146
We have investigated the electronic structure and the Fermi surface of SnO using density functional theory calculations within
recently proposed exchange-correlation potential (PBE + mBJ) at ambient conditions and high pressures up to 19.3 GPa where
superconductivity was observed. It was found that the Sn valence states (5s, 5p, and 5d are strongly hybridized with the O 2p states, and that our density functional theory calculations are in good agreement with O K-edge X-ray spectroscopy measurements for both occupied and empty states. It was demonstrated that the metallic states appearing
under pressure in the semiconducting gap stem due to the transformation of the weakly hybridized O 2p-Sn 5sp subband corresponding to the lowest valence state of Sn in SnO. We discuss the nature of the electronic states involved in
chemical bonding and formation of the hole and electron pockets with nesting as a possible way to superconductivity. 相似文献
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10.
In this paper, we calculate the band gap and the band discontinuities of a GaN
y
AsBi
x
structure lattice matched to GaAs substrate using the conduction and the valence band anticrossing models at the same time.
The results obtained show a good agreement with experiment. The nitrogen and the bismuth concentrations leading to a wavelength
emission of 1.55 μm have been determined (x = 3.5%, y = 2%). This structure shows a good electron confinement resulting in a high characteristic temperature. 相似文献
11.
D. B. Lu Y. L. Song Z. X. Yang H. R. Xu C. Wang Z. H. Gao 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,84(3):419-424
By using the first-principles calculations, the electronic properties are studied for the
F-terminated SiC nanoribbons (SiCNRs) with either zigzag edges (ZSiCNRs) or armchair edges
(ASiCNRs). The results show that the broader F-terminated ZSiCNRs are metallic and the
edge states appear at the Fermi level, while the F-terminated ASiCNRs are always
semiconductors independent of their width but the edge states do not appear due to the
Si-C dimer bonds at the edges. The charge density contours analyses shows that the Si-F
and Si-C bonds are all ionic bonds due to the much stronger electronegativities of the F
and C atoms than that of the Si atom. However, the C-F bonds display a typical non-polar
covalent bonding feature because of the electronegativity difference between the F and C
atoms of 1.5 is a much smaller than that of between the F and Si atoms of 2.2, as well as
the tighter bounded C 2s
22p
2
electrons with smaller orbital radius than the Si
3s
23p
2 electrons. For both the
F- and the H-terminated ZSiCNRs, the ground state is a ferromagnetic semiconductor. 相似文献
12.
The electronic structure of (111) surface of β-crystobalite is investigat ed using the empirical tight binding method. Our calculations identify surface states in the conduction band, band gap and valence band. The surface state formed from silicon-s and pz orbitals, which is believed to account for the structure in the O K excitation spectra, lies in the band gap. It is seen that oxygen adsorption on the surface removes surface states and gives rise to a sharp peak at about — 3.8 eV below the valence band edge. 相似文献
13.
Erich Steiner 《Molecular physics》2013,111(4):669-681
An orbital-fitting procedure has been used to fit the s- and p-orbitals expressed in terms of a cusped gaussian basis onto Clementi's accurate SCF orbitals. The results suggest that approximately double-zeta accuracy may be obtained for the s-orbitals with a basis of two 1s gaussians per orbital supplemented by a single 1s cusp function for the representation of the orbitals at and near the nucleus, and for the p-orbitals with a basis of three 2p gaussians per orbital plus the 2p cusp function. It is proposed that for the s-orbitals the cusped gaussian basis is superior to both the all-gaussian and Slater function bases for the purpose of molecular calculations. The results are less conclusive for the p-orbitals and, although the efficiency of the basis increases with increasing nuclear charge, further investigation is necessary before a definite conclusion may be reached as to the usefulness of the cusped gaussian basis for the representation of p-orbitals. 相似文献
14.
Summary Using the Green's function method, the superconducting gap equation in the Anderson model with nearest-enighbour attraction
between correlated electrons is obtained. Thes- andp-wave solutions of this equation have been analysed for different choices of the parameters of the model.
In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching. 相似文献
15.
R. Gonczarek M. Krzyzosiak A. Gonczarek 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(3):299-308
In this paper we find and present on diagrams in the coordinates of η=2t1/t0 (the ratio of the second and the first nearest
neighbor hopping integrals) and n (the carrier concentration) the
areas of stability for the superconducting spin-singlet s-
and d-wave and the spin-triplet p-wave order
parameters hatching out during the phase transition from the normal
to the superconducting phase. The diagrams are obtained for an
anisotropic two-dimensional superconducting system with a relatively
wide partially-filled conduction band. We study a tight-binding
model with an attractive nearest neighbor interaction with the
amplitude V1, and the on-site interaction (with the amplitude
V0) taken either as repulsive or attractive. The problem of the
coexistence of the s-, p- and d-wave order
parameters is addressed and solved for chosen values of the ratio
V0/V1. A possible island of stability of the d-wave
order parameter in the s-wave order parameter environment for
a relatively strong on-site interaction is revealed. The triple
points, around which the s-, d-, and p-wave
order parameters coexist, are localized on diagrams. It is shown
that results of the calculations performed for the two-dimensional
tight-binding band model are dissimilar with some obtained within
the BCS-type approximation. 相似文献
16.
In this study, we have investigated the stability and conductivity of unsupported, two-dimensional infinite gold nanowires
using ab initio density functional theory (DFT). Two-dimensional ribbon-like nanowires with 1–5 rows of gold atoms in the
non-periodic direction and with different possible structures have been considered. The nanowires with >2 rows of atoms exhibit
dimerization, similar to finite wires, along the non-periodic direction. Our results show that in these zero thickness nanowires,
the parallelogram motif is the most stable. A comparison between parallelogram- and rectangular-shaped nanowires of increasing
width indicates that zero thickness (111) oriented wires have a higher stability over (100). A detailed analysis of the electronic
structure, reveals that the (111) oriented structures show increased delocalization of s and p electrons in addition to a stronger delocalization of the d electrons and hence are the most stable. The density of states show that the nanowires are metallic and conducting except
for the double zigzag structure, which is semiconducting. Conductance calculations show transmission for a wide range of energies
in all the stable nanowires with more than two rows of atoms. The conductance channels are not purely s and have strong contributions from the d levels, and weak contributions from the p levels. 相似文献
17.
G. Puddu 《The European Physical Journal A - Hadrons and Nuclei》2007,34(4):413-415
We compare the recent exact and coupled-cluster calculations (Phys. Rev. Lett. 98, 112501 (2007)) of energy levels using the GXPF1A Hamiltonian modified with variable shell gap with the corresponding results
obtained with the hybrid multi-determinant scheme. We show that the hybrid multi-determinant scheme is highly cost-efficient
and very accurate for several angular momenta and variable shell gap of the f5/2, p3/2, p1/2 shells relative to the f7/2 shell. 相似文献
18.
We report for the first time the Compton profiles of electron momentum distribution inβ-gallium calculated along the crystallographic directions (100), (110) and (111). The conduction electron states for this
purpose are determined in the energy band calculations using model potential. The core states, on the other hand, are represented
each by a single tight-binding function. The results show that the Compton profiles are nearly isotropic with very little
directional dependence, which is suggestive of a free-electron-like distribution of the conduction electrons in this system.
The latter conclusion is in close confirmity with similar conclusions drawn in augmented plane wave (APW) calculation of energy
bands and the derived Knight-shift results inβ-Ga. 相似文献
19.
The interaction of conduction and valence bands in narrow gap semiconductors such as InSb and HgCdTe influences the position and width of subband energy levels in space-charge layers. While a nonzero width can only occur if electrons from the conduction band can tunnel into approximately degenerate states of the valence band the level shifts due to band mixing are always present. We present a Green's function treatment which allows in a simple way to discuss the dependence of band mixing effects on the parameters of thek·p-Hamiltonian in particular the band gap. The essential qualitative feature of the level shifts is adecrease of subband energy separation withdecreasing effective mass. This agrees with recent experimental results for Hg1-x
Cd
x
Te. 相似文献
20.
Hartree-Fock (HF) calculations have been performed fcr 12C nucleus assuming a trigonal D3h equilibrium configuration. Different aspects including symmetry, kinds of two-body interactions are investigated. The HF calculations have been carried out using a velocity dependent effective potential of s-wave interaction. The results are compared with previous calculations. In all HF calculations no deviation from axial symmetry is obtained. 相似文献