共查询到20条相似文献,搜索用时 46 毫秒
1.
We calculate the ground state of the half-filled Hubbard model and its energy by starting from a spindensity wave approximation and improving it by incorporating transverse spin fluctuations. The calculations are done by employing a projection method. The quality of the proposed approximation is particularly high for intermediate and large Coulomb repulsion U, where it exceeds considerably e.g. that of the Gutzwiller projected spin-density wave state. To order t
2/ U (where t is the hopping matrix element), our approximation is shown to be equivalent to a recent Coupled Cluster calculation for the Heisenberg antiferromagnet. Finally we show how to order t
2/ U the linear spin-wave approximation for the Heisenberg antiferromagnet may be obtained. 相似文献
2.
We use a 4ħ Ω shell-model calculation with a two-body effective interaction derived microscopically from the Reid93 potential to calculate
the isospin-mixing correction for the 10C→ 10B superallowed Fermi transition. The effective interaction takes into account the Coulomb potential as well as the charge
dependence of T=1 partial waves. Our results suggest the isospin-mixing correction δ
c ≈ 0.1%, which is compatible with previous calculations obtained by other methods. The obtained δ
C correction is about a factor of four too small to obtain unitarity of the Cabibbo-Kobayashi-Maskawa matrix with the present
experimental data.
Presented by B.R. Barrett at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5,
1997.
This work is supported in part by NSF grant No. PHY96-05192. 相似文献
3.
We present a method to calculate two- and three-body amplitudes including the Coulomb potential in a momentum space. Our aim is to obtain the exact two-body Coulomb amplitudes used in three-body calculations, which reproduce the analytic phase shifts. For the purpose, our theory is based on the modified Coulomb potential (MCP) whose Fourier transformation is equivalent to the pure Coulomb potential in a configuration space, and the two-potential theory with an auxiliary potential. Moreover, one can analytically determine a decisive range R dec in the MCP. By using the MCP, we obtain the two-body Coulomb modified nuclear amplitude as well as the pure Coulomb amplitude. The calculated phase shift are very good fitting with the experimental data. 相似文献
4.
We use the relativistic configuration-interaction method and the model potential method to calculate the scalar and tensor
components of the dipole polarizabilities for the excited states 1 s3 p
3
P
0 and 1 s3 p
3
P
2 of the helium atom. The calculations of the reduced matrix elements for the resonant terms in the spectral expansion of the
polarizabilities are derived using two-electron basis functions of the relativistic Hamiltonian of the atom, a Hamiltonian
that incorporates the Coulomb and Breit electron-electron interactions. We formulate a new approach to determining the parameters
of the Fuss model potential. Finally, we show that the polarizability values are sensitive to the choice of the wave functions
used in the calculations.
Zh. éksp. Teor. Fiz. 115, 494–504 (February 1999) 相似文献
5.
We have measured the branching ratio for the isospin-forbidden Fermi β-decay of 28Mg to the 0.972 MeV 0 +, T = 1 level in 28Al. This decay occurs through an admixture of the 0 +, t = 2 analog state at 5.992 MeV into the anti-analog level at 0.972 MeV. A charge-dependent matrix element of 17.0 ?5.8+4.3 keV is deduced from the observed (0.21 ± 0.12)% branch. Comparisons are made with matrix elements deduced in other nuclei. An analysis based on a simple shell model with fourfold degenerate Orbitals indicates the importance of the two-body Coulomb interaction in isospin mixing in nuclei with more than one valence proton. 相似文献
6.
Effects of the spin-orbit Hamiltonian HLS , including both the spin-same orbit and spin-other orbit terms, are studied at the self consistent field (SCF) level of theory. Separate calculations are carried out for each state considered, and biorthogonal orbitals are constructed for the evaluation of matrix elements. Doublet-doublet and singlet-triplet interactions are discussed. The evaluation of the Gaussian basis function integrals is described in a Cartesian component representation, these integrals being directly related to one and two electron second derivative integrals. This new SCF spin-orbit code is used to ( i) determine the spatial dependence of the spin-orbit parameters for the Renner-Teller 2B 1, 2A 1 states of H 2O +, ( ii) determine the spin-orbit splitting of the 2Π states of OH as a function of bond-length and ( iii) calculate the radiative lifetime of the a 3Σ + state of NO +. In each case these calculations are compared with more sophisticated configuration interaction studies, but it is found that the evaluation of these effects near equilibrium geometries at the SCF level is sufficiently accurate, provided that a large basis set is used. 相似文献
7.
ABSTRACTThe pair functions that minimise the correlation energy of second-order many-body perturbation (MP2) theory (the Hylleraas functional) are obtained as solutions to the corresponding Sinano?lu equation by expanding them on a six-dimensional, multicentre, radial-angular grid of two electrons. Cusps in the pair functions at the nuclei are described numerically accurately by the multicentre grid. A cusp in each singlet pair function at the coalescence of the two electrons is taken into account analytically by a correlation factor. With a grid of approximately 10,000 points per atom, the MP2 correlation energies for atoms and polyatomic molecules are obtained usually within 0.1 m E h of the complete-basis-set results. The correlation factor, auxiliary basis functions, and a judicious choice of integration algorithms are all necessary to stabilise the grid-based MP2 and underlying Hartree–Fock (HF) calculations. The auxiliary basis set, in particular, largely restores the hermiticity and diagonal dominance of the Fock matrix as well as furnishes virtual orbitals used in a resolution-of-the-identity approximation to lower the dimension of some integrals. The results of the grid-based HF and MP2 calculations without a correlation factor are found to suffer from large, nonsystematic errors frequently. 相似文献
8.
A general theory for constructing a weak Markov dilation of a uniformly continuous quantum dynamical semigroup T
t
on a von Neumann algebra ? with respect to the Fock filtration is developed with the aid of a coordinate-free quantum stochastic
calculus. Starting with the structure of the generator of T
t
, existence of canonical structure maps (in the sense of Evans and Hudson) is deduced and a quantum stochastic dilation of
T
t
is obtained through solving a canonical flow equation for maps on the right Fock module ?⊗Γ( L
2(ℝ +, k
0)), where k
0 is some Hilbert space arising from a representation of ? ′. This gives rise to a *-homomorphism j
t
of ?. Moreover, it is shown that every such flow is implemented by a partial
isometry-valued process. This leads to a natural construction of a weak Markov process (in the sense of [B-P]) with respect
to Fock filtration.
Received: 15 June 1998/ Accepted: 4 March 1999 相似文献
9.
Off-the-shell anomalous factors of the two-body Coulomb transition matrices appear in the integral form of the Faddeev second-order
nuclear-electronic amplitude, for proton-hydrogen charge transfer scattering in a typical nlm → n′ l′ m′ transition. A symmetric-impulse approximation (SIA) is applied to eliminate these factors and an induction method is proposed
to analytically calculate the remaining integrals. The nuclear-electronic amplitude is derived for the general case, and for
totally symmetric collisions, in terms of generalized hypergeometric functions of two variables, F
4, and of one variable, 3
F
2, respectively. The angular distribution of the second-order nuclear-electronic charge transfer amplitude shows the Thomas
mechanism as a peak or a hump for symmetric and asymmetric collisions. There also exists a peak in the forward angular distribution
of the second-order nuclear-electronic amplitude, which partly cancels the kinematic peak in the angular distribution of the
charge transfer differential cross sections. 相似文献
10.
An eikonal expansion is used to provide systematic corrections to the eikonal approximation through order 1/ k
2, where k is the wave number. Electron wave functions are obtained for the Dirac equation with a Coulomb potential. They are used to
investigate distorted-wave matrix elements for quasi-elastic electron scattering from a nucleus. A form of effective-momentum
approximation is obtained using trajectory-dependent eikonal phases and focusing factors. Fixing the Coulomb distortion effects
at the center of the nucleus, the often-used ema approximation is recovered. Comparisons of these approximations are made with full calculations using the electron eikonal
wave functions. The ema results are found to agree well with the full calculations. 相似文献
11.
A method by means of which the two-body short-range correlations in the nucleon-nucleon interaction are taken accurately into account in three-body bound-state calculations is described. The method is independent of the nucleon-nucleon interaction. We employ our method to calculate meson-exchange corrections to the magnetic moments of 3H and 3He and the Coulomb energy of 3He. 相似文献
12.
A comparison is made of the accuracy with which the total electronic energy can be calculated by using the finite basis set approach (the algebraic approximation) and the finite difference method in calculations employing the Hartree—Fock model for the open shell ground ( X 2Σ +) states of the fluorides BaF and YbF. The convergence of the calculations carried out within the algebraic approximation is monitored by employing systematically constructed basis sets of increasing size. The difference between the finite basis set and finite difference Hartree—Fock energies is 2.6μ E h for BaF and 2.8μ E h for YbF. Dipole moments determined within the algebraic approximation are also compared with the corresponding finite difference expectation values. 相似文献
13.
We discuss effective field-theory treatments of the problem of three particles interacting via short-range forces (range R ≪ a
2, with a
2 the two-body scattering length). We show that forming a once-subtracted scattering equation yields a scattering amplitude
whose low-momentum part is renormalization-group invariant up to corrections of O( R
3/ a
2
3). Since corrections of O( R/ a
2) and O( R
2/ a
2
2) can be straightforwardly included in the integral equation’s kernel, a unique solution for 1 + 2 scattering phase shifts
and three-body bound-state energies can be obtained up to this accuracy. We use our equation to calculate the correlation
between the binding energies of Helium-4 trimers and the atom-dimer scattering length. Our results are in excellent agreement
with recent three-dimensional Faddeev calculations that used phenomenological inter-atomic potentials. 相似文献
14.
The orbital amplitude difference function is used to assess the quality of Hartree–Fock orbitals obtained by invoking the algebraic approximation for the BF ground-state. Systematic sequences of even-tempered, spherical-harmonic Gaussian-type basis functions are used to generate orbitals for which the corresponding total Hartree–Fock energy approaches the 1 μ E h level of accuracy. Exact orbitals are obtained from finite difference calculations using a grid based on spheroidal coordinates. The finite basis set approximations for the orbital are discretized. The accuracy of the discretization is assessed. For each occupied orbital a discretized representation of the orbital amplitude difference function is generated and analysed. 相似文献
15.
Exact analytical representation for the Coulomb matrix elements by means of Appell’s double series F2 is derived. The finite sum obtained for the Appell function F2 allows us to evaluate explicitly the matrix elements of the two-body Coulomb interaction in the lowest Landau level. An application requiring the matrix elements of Coulomb potential in quantum Hall effect regime is presented. 相似文献
16.
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
17.
Theoretical estimates for the astrophysical S-factor and the rate of the reaction d(α, γ)6Li were obtained on the basis of the two-body model involving an α−d potential that has a simple Gaussian form and which describes correctly S-, P-, and D-wave phase shifts, the binding energy, and the asymptotic normalization coefficient for the S-wave bound state. The wave functions for the bound and continuum channels were calculated with the aid of the highly precise Numerov algorithm. The results for the contributions of the E1 and E2 transition components reveal a good convergence as the upper limit in the effective integrals increases up to 40 fm. The results obtained for the astrophysical S-factor and the rate of the reaction d(α, γ)6Li in the temperature range of 106
K ≤ T ≤ 1010 K agree well with the results of the calculations performed by A.M. Mukhamedzhanov and his coauthors [Phys. Rev. C 83, 055805 (2011)] by using the known asymptotic form of the wave function at low energies and a complicated two-body potential at higher energies. 相似文献
18.
The structure of the low-lying states of 58Ni has been calculated in shell model by assuming an inert 56Ni core plus two valence nucleons in the p 3/2, f 5/2 and p 1/2 orbitals. The two-body matrix elements are first expressed in terms of seven radial matrix elements and these are then parametrized to give best fit between the computed and the observed energies of the levels below 4 MeV. The wave-functions obtained using these two-body matrix elements are used to study the concept of effective charges. It is found that a single effective charge is not sufficient to predict the B(E2) rates equally well for the thirteen known transitions for which experimental values are available. Assumption of state-dependent effective charges gives a far better agreement. An analysis using wavefunctions obtained with Kuo’s two-body matrix elements also gives a similar result. 相似文献
19.
We extend our approach to incorporate the proton-proton ( ppCoulomb force into the three-nucleon (3 NFaddeev calculations from elastic proton-deuteron ( pdscattering to the breakup process. The main new ingredient is a 3-dimensional screened pp Coulomb t -matrix obtained by a numerical solution of the 3-dimensional Lippmann-Schwinger (LS) equation. We demonstrate numerically
that the proton-deuteron ( pdbreakup observables can be determined from the resulting on-shell 3 N amplitudes increasing the screening radius. However, contrary to the pd elastic scattering, the screening limit exists only after renormalisation of the pp
t -matrices. 相似文献
20.
The relaxation of the specific heat and the entropy to their equilibrium values is investigated numerically for the three-dimensional
Coulomb glass at very low temperatures. The long time relaxation follows a stretched exponential function, f ( t) = f
0exp - ( t/τ) β
, with the exponent β increasing with the temperature. The relaxation time diverges as an Arrhenius law when T→ 0.
Received 24 May 2001 and Received in final form 12 September 2001 相似文献
|