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1.
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
2.
Graham R. Underwood 《Molecular physics》2013,111(4):729-730
A series of one-electron properties, i.e. dipole, quadrupole, octupole moments, diamagnetic susceptibility, second moments and second moment anisotropies of charge distribution, electric field, electric field gradient, diamagnetic shielding, nuclear quadrupole coupling constant, have been obtained by ab initio S.C.F. calculations for the molecules COF2, SO2F2 and SOF2. The effect of the size of the gaussian basis sets, including d-type polarization functions, as well as the contraction schemes on the latter properties have been studied for the COF2 molecule. This study enables us to determine the basis giving the best results as compared to experiment. With this basis the calculations have been extended to the properties of the molecules SO2F2 and SOF2. Good overall agreement with experiment is obtained. 相似文献
3.
Single crystals of the cobalt skutterudites CoP3, CoAs3 and CoSb3 have been prepared by the chemical vapor transport technique using chlorine as the transport agent. Chemical analysis and density measurements were used to determine accurately the stoichiometry of these crystals. Physical properties of chemically pure single crystals were obtained by X-ray diffraction, magnetic susceptibility and electrical measurements. CoP3 is a diamagnetic semiconductor with an optical band gap of 0.45 eV. CoAs3 and CoSb3 are also diamagnetic and show an increase in their resistivity as a function of increasing temperature. In addition, they do not give any measurable absorption edge but absorb radiation at all frequencies from 0.4 to 4.3 eV. 相似文献
4.
In this study, the effects of quantum confinement and effective mass anisotropy parameter on the diamagnetic susceptibility of a hydrogenic donor placed in GaAs, Si, and Ge quantum wells with infinite confinement potential are investigated in the effective mass and parabolic band approximations by using two and one parameter trial wave functions. It is observed that the diamagnetic susceptibility of a hydrogenic donor in anisotropic quantum wells is essentially equal to the transverse diamagnetic susceptibility part when well widths are larger than L > 100 Å, and the impurity is located at center. Moreover, a two parameter trial wave function model gives higher values of diamagnetic susceptibility, except for χz (GaAs). 相似文献
5.
S. F. J. Cox N. Ayres De Campos P. J. Mendes J. M. Gil A. Kratzer V. M. Nield J. A. S. Smith 《Hyperfine Interactions》1994,86(1):747-752
Level crossing resonance studies of ice, doped with HF and NH3 to enhance and suppress the concentration of orientational defects, support the hypothesis that muons can trap at such defects to form complexes of the type H2O-Mu+-OH2. The doping alters the partition of the total diamagnetic fraction between this state, which is stable against charge migrationvia proton rearrangement at low temperature, and the neutral HMuO state, the isotopically substituted water molecule. 相似文献
6.
The influence of additions of gold (5 and 10 at. %) on the lattice parameters, the superconducting transition temperature,
and the diamagnetic susceptibility of the high-temperature superconducting ceramic YBa2Cu3O7−δ
is investigated. The influence of gold on the kinetics of the release of weakly bound oxygen during heating of the ceramic
in a vacuum is also studied. It is shown that doping the ceramic with gold causes uniaxial expansion of the lattice of the
material, a significant decrease in the diamagnetic susceptibility, and nonmonotonic variation of the kinetic parameters of
the oxygen release, while the superconducting transition temperature remains nearly unchanged.
Zh. Tekh. Fiz. 67, 31–34 (February 1997) 相似文献
7.
D. Geist 《Zeitschrift für Physik A Hadrons and Nuclei》1960,157(4):490-498
For semiconductors it is possible, to determine the contribution of the free carriers to the magnetic susceptibility. Holes in silicon (density 1018 to 1019cm?3) have at 297 and 141° K a small paramagnetic susceptibility. In contrast, one computes from cyclotron mass parameters for 4° K a strong diamagnetic susceptibility. Holes in germanium (density 4 · 1017 and 4 · 1019 cm?3) have a diamagnetic susceptibility, which is much smaller, than one would expect from cyclotron resonance masses. — Neutral boron atoms contribute in small concentration at 141 °K to the susceptibility. 相似文献
8.
Besides the well-known bulk fluctuation contribution to the diamagnetic susceptibility there is an additional surface contribution with the singularity at TSH exceeding the superconducting bulk transition temperature Tc(H). The results obtained allow to explain the anomalous behavior of the diamagnetic susceptibility found by Khaikin and Khlyustikov. 相似文献
9.
10.
The effect of temperature and pressure, simultaneously, on the diamagnetic susceptibility and binding energy of a hydrogenic donor impurity at the center of a GaAs/Ga1−xAlxAs quantum antidot is studied within the effective mass approximation. For this goal, we first analytically solve the Schrödinger equation to obtain wavefunctions and energy levels. Then, using the electronic states, we can calculate the diamagnetic susceptibility. The results obtained from the present work reveals that (i) the diamagnetic susceptibility increases with increasing pressure, (ii) the diamagnetic susceptibility decreases by increasing temperature, (iii) the value of 〈r2〉 decreases with increasing pressure due to the quantum confinement, and (iv) an increase in the pressure enhances the binding energy for a constant temperature. 相似文献
11.
The radial distribution function can be expressed in a virial expansion. Using the 6 : 12 potential the second-order density coefficient, g 2(r), is numerically calculated for a wide range of temperatures and intermolecular separations. These results are used to calculate the second-order density coefficient, c 2(r), in the expansion of the direct correlation function and to calculate the fourth virial coefficient, B 4. In addition, approximate results for g 2(r), c 2(r), and B 4 are calculated on the basis of the Percus-Yevick, hypernetted chain, and the self-consistent approximations of Hurst and Rowlinson. These approximate results are compared with the exact results. The Percus-Yevick theory is in good agreement with the exact results at high temperatures but is unsatisfactory at low temperatures. The hyper-netted-chain approximation is in fair agreement with the exact results at high temperatures, is in poor agreement at intermediate temperatures, but is in good agreement at low temperatures. The self-consistent approximations are in reasonably good agreement with the exact calculations at all temperatures. 相似文献
12.
A quantum-mechanical study is made of the changes of the nuclear magnetic screening constant σ and the diamagnetic susceptibility X of two interacting hydrogen atoms due to van der Waals and overlap interatomic forces (effects of electron spin being neglected). At large distances the calculations show that van der Waals forces decrease the nuclear screening but increase the diamagnetic susceptibility (in magnitude). As the internuclear distance is reduced the first effect of overlap forces is to increase the screening in the repulsive (electronic triplet) state but this is followed by a further reduction. Attractive overlap forces (as in the ground state of H2) ultimately lead to an increase in screening. 相似文献
13.
利用数值模拟程序模拟了不同高度核爆炸下大气的X射线电离及演化过程.结果表明: X射线电离产生的电子数密度在射线到达后约100 ns时刻达到峰值, 峰值数密度随着到裸核区距离的增加而减小;电子具有较长的寿命, 电子寿命随着到裸核区距离的增加而增大; X射线电离空气产生正离子O+, O2+, N2+,爆高为120 km情况下 O+的峰值数密度与O2+的相近,能维持约1 s. X射线对空气的电离影响范围在数十千米以内,在距裸核区较近的区域, 爆高为80 km时产生的电子峰值数密度比爆高为120 km时的电子峰值数密度高, 在距裸核区较远的区域则相反. 相似文献
14.
Dr. L. Wehrli 《Zeitschrift für Physik B Condensed Matter》1968,8(2):87-128
We have measured and discussed the field independent magnetic properties of Bi1-xSbx alloys for the concentration range 0≦x≦0,4. The observed transitions from the semimetal to semiconductor phase at about 7 At.-% Sb and from the semiconductor to semimetal phase at about 22 At.-% Sb are very well defined. Measurements on the semiconductor phase at low temperatures allowed us to separate the lattice componentχ G of the susceptibility from that due to the charge carriersχ L. It is therefore possible to estimate these two components for pure Bi. The results show thatχ G is strongly diamagnetic in all crystall directions and thatχ L is paramagnetic. An estimate of the charge carrier susceptibility based on a modified Pauli Landau model is found to give an order of magnitude agreement with the experimental results. The deviation can be attributed to a nonparabolic conduction band. The dependence of the energy gapΔE on the Sb concentration has also been determined. 相似文献
15.
G. Rezaei N.A. Doostimotlagh 《Physica E: Low-dimensional Systems and Nanostructures》2012,44(4):833-838
Electric field, hydrostatic pressure and conduction band non-parabolicity effects on the binding energies of the lower-lying states and the diamagnetic susceptibility of an on-center hydrogenic impurity confined in a typical GaAs/AlxGa1−xAs spherical quantum dot is theoretically investigated, by direct diagonalization of the Hamiltonian. To this end, the effect of band non-parabolicity has been performed, by means of the Luttinger-Kohn effective mass equation. Binding energies and diamagnetic susceptibility of the hydrogenic impurity are computed as a function of the dot size, external electric field strength and hydrostatic pressure, with considering the edge-band non-parabolicity. Results show that the external electric field and the hydrostatic pressure have an obvious influence on the binding energies and the diamagnetic susceptibility of the impurity. 相似文献
16.
Amand Faessler J. E. Galonska K. Goeke 《Zeitschrift für Physik A Hadrons and Nuclei》1972,250(5):436-445
The charge distribution of208pb calculated in the Hartree-Fock (HF) approach using the density dependent nucleon-nucleon interaction of Ehlers and Moszkowski is tested by simultaneous comparison with experimental data from 502 MeV elastic electron scattering and muonic atoms. In both cases the agreement is very good and nearly as good as the best fits with a phenomenological charge distribution of Fermi type, if the effect of the polarization of the nucleus due to the presence of the muon is properly taken into account. In contradiction to the Fermi fits the HF distribution shows a hump at the center of the nucleus. 相似文献
17.
P. Nithiananthi 《Solid State Communications》2006,137(8):427-430
The binding energies of a hydrogenic donor both in the parabolic and non-parabolic conduction band model within the effective mass approximation have been computed for the low-dimensional semiconducting systems (LDSS) like quantum well, quantum well wire and quantum dot taking GaAs/AlxGa1−xAs systems as an example. It is observed that the effect of non-parabolicity is not effective when the system goes to lower dimensionality. The diamagnetic susceptibility of a hydrogenic donor impurity has also been computed in these LDSS in the infinite barrier model. Since no theoretical or experimental works on the diamagnetic susceptibility of LDSS are available in the literature, as a realistic case the diamagnetic susceptibility has been computed in the finite barrier model (x=0.3) for a quantum well and the results are discussed in the light of semiconductor-metal transition. 相似文献
18.
Vladimir A. Kulbachinskii Boris M. Bulychev Vladimir G. Kytin Alexey V. Krechetov Valeriy P. Tarasov Elizaveta A. Konstantinova Yuriy A. Velikodnyi Yuriy B. Muravlev Andrey V. Zoteev 《Central European Journal of Physics》2010,8(1):101-112
Sodium fullerides Na
n
C60 (n = 2, 3) have been synthesized by a liquid phase reaction and investigated with X-ray diffraction (XRD), nuclear magnetic
resonance (NMR), electron paramagnetic resonance, and differential thermal analysis. XRD data indicate that the crystal structure
of Na2C60 at 300 K is face centered cubic (FCC). A phase transition from primitive cubic to FCC crystal structure has been observed
in this work in Na2C60 fulleride at 290 K. The transition is accompanied by the step-like change of paramagnetic susceptibility. The crystal structure
of Na3C60 is more complicated than, and different from, what has been reported in the literature. A nearly seven-fold increase of paramagnetic
susceptibility with increasing temperature has been observed in the Na3C60 fulleride at 240–260 K. In the same temperature range, a new line at about 255 ppm appears in the 23Na NMR spectrum, indicating a significant increase of electron density near the Na nucleus. The observed effect can be explained
by a metal-insulator transition caused by a structural transition. 相似文献
19.
Measurements of the diamagnetic susceptibility χ at room temperature are reported for Ge1-xSx and Ge1-xSex amorphous alloys as a function of composition. The composition dependence of χ is shown to reflect the corresponding changes in the average gap Eg and it is concluded that the dia diamagnetic enhancement observed in tetrahedrally bonded amorphous semiconductors is caused by a decrease in the interband matrix element in the Van-Vleck paramagnetic susceptibility term with bond angle distortion rather than changes in Eg. 相似文献
20.
A theoretical approach for the calculation of hyperfine parameters in solids from first principles is presented. These calculations are based on the full potential linearized-augmented-plane-wave (LAPW) band structure method, which is currently one of the most accurate schemes to determine the electronic structure in ordered solids. Exchange and correlation is treated within density functional theory using the generalized gradient approximation. Once the electron density is calculated self-consistently with high accuracy, quantities like electric field gradients (EFG), isomer shifts or hyperfine fields can easily be obtained from this density without further approximations. Using this approach we have studied various systems including metals, insulators, ionic compounds or the highT
c superconductors. In general we find good agreement between theory and experiment, which proves that our method is very accurate. Having these results in mind we are confident that this method is accurate enough to determine the value of the nuclear quadrupole momentQ, provided experimental measurements of the quadrupole coupling constant are available. This procedure is demonstrated forQ of77Se and100Rh, two nuclei recently used in PAC measurements. An extensive study of EFGs at Fe sites in various Fe-compounds has been performed leading to a very reliable quadrupole moment ofQ(57Fe)=0.16 b, a value twice as large as that deduced from recent HF calculations but back to older estimates. 相似文献