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Showing papers on "Random phase approximation published in 1981"



Journal ArticleDOI
TL;DR: In this article, the first consistent random phase approximation with exchange (RPAE) calculation of Mn photoionisation in the giant resonance region is reported and a satisfactory agreement with experiment has been achieved and the autoionisation nature of the experimentally observed maximum in the cross section is confirmed.
Abstract: The first consistent random phase approximation with exchange (RPAE) calculation of Mn photoionisation in the giant resonance region is reported. In order to be able to perform these calculations, the atomic electrons were separated into two groups called 'up' and 'down' depending on their spin projection. A satisfactory agreement with experiment has been achieved and the autoionisation nature of the experimentally observed maximum in the cross section is confirmed.

28 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of mean-field fluctuations on the nuclear level density is investigated along with the usual effects of temperature and chemical potential fluctuations together with generalized random phase approximation correlations and produce bosonlike terms in the nuclear entropy.
Abstract: Functional integral formulation of the mean-field approximation for many-body systems is used to study the nuclear partition function Both static and dynamic mean-field solutions with statistical occupations of the single particle wave functions are discussed These correspond to different physical processes in the nuclear system In the static case the effect of mean-field fluctuations on the nuclear level density is exhibited This effect enters consistently along with the usual effects of temperature and chemical potential fluctuations Together they account for generalized random phase approximation correlations and produce bosonlike terms in the nuclear entropy Because of the self-consistency of the approach, no overcounting of the collective and single-particle degrees of freedom occurs The effects of the single particle continuum are included in the discussion In the low temperature limit a simple correction to the level density parameter is evaluated, which leads to an increase of its magnitude Consequences of a possible multiplicity of static mean-field configurations are briefly discussed Dynamical mean-field solutions are considered in relation to compound nucleus fission They provide the extension of the mean-field description of spontaneous fission given recently A microscopic expression for the energy dependence of the average fission width is presented It combines both themore » dynamical and statistical features of the tunneling mean-field solution in the subbarrier region« less

27 citations


Journal ArticleDOI
TL;DR: In this article, the Fano parameters of the 3s−14p autoionization profile in argon have been calculated in different approximations and the best results have been obtained when many-electron correlations in the random phase approximation as well as complicated "twoelectron-two-hole" excitations were taken into account.

21 citations


Journal ArticleDOI
TL;DR: The coupling of the solutions to the random phase approximation pairing vibration and the collective quadrupole oscillation, obtained from a boson expansion approach, is used to describe simultaneously many properties of the even-even isotopes of Ge as discussed by the authors.
Abstract: The coupling of the solutions to the random phase approximation pairing vibration and the collective quadrupole oscillation, obtained from a boson expansion approach, is used to describe simultaneously many properties of the even-even isotopes of Ge. Low lying energies, E0 and E2 transitions, two nucleon transfer amplitudes, and quadrupole moments are calculated and fairly good agreement is obtained compared to experiment. In particular the behavior of the 0/sup +//sub 2/ state energy as a function of mass is accurately described including the prediction of its being the lowest energy excited state of /sup 72/Ge. The shape of the nucleus is concluded to be in a transitional region between prolate and oblate.

19 citations


Journal ArticleDOI
TL;DR: In this paper, a theory for internal energy redistribution in polyatomic molecules perturbed by strong radiation fields is constructed using stochastic theory, which assumes that a random phase approximation is valid after appropriate time intervals.
Abstract: A theory for internal energy redistribution in polyatomic molecules perturbed by strong radiation fields is constructed. Use is made of stochastic theory, which assumes that a random phase approximation is valid after appropriate time intervals. This approximation permits the Schrodinger equation to be replaced with a finite‐difference master equation for the probabilities of occupying the various quantum levels. The semiclassical theory of the radiation–molecule interaction is employed in this work. A laser line profile is incorporated in the formalism, and this is used to simulate the effects of rotational states and collisions. At each stochastic step the energy changes in the molecules due to radiation are estimated. Thus, energy conservation is explicitly taken into account. Model calculations for SO2, whose transition dipole moment matrix elements and anharmonic force constants have been determined, indicate a complex interplay of anharmonic and radiative coupling. Power density, laser linewidth, an...

12 citations


Journal ArticleDOI
TL;DR: In this article, the excitation energies in the random phase approximation with exchange can be found from the linearised equations of motion of electron-hole pairs in a real space representation in which many-body interactions and one-electron hopping are treated on the same footing.
Abstract: The excitation energies in the random phase approximation with exchange can be found from the linearised equations of motion of electron-hole pairs. This is expressed in a real space representation in which many-body interactions and one-electron hopping are treated on the same footing. In the real space representation both the direct and exchange interactions between electron-hole pairs are included, so excitons, plasmons and single-particle excitations are all contained in the formalism. This is applied to a model insulator, first without one-electron hopping: this shows a dispersive Frenkel exciton and charge transfer excitations. When one-electron hopping is included, the Frenkel exciton can lie within the single-particle continuum; the charge transfer states become Wannier excitons. Applied to metals, the real space technique gives exactly the same plasmon frequency as the usual dielectric function method.

10 citations


Journal ArticleDOI
TL;DR: In this article, critical conditions for instability in the isovector unnatural parity channel in nuclei are investigated in terms of the random-phase approximation, and it is found that the nonresonant part of the iterated two-pion exchange moves the characteristics of the nuclear phase transition closer to those for rho meson condensation.
Abstract: Critical conditions for instability in the isovector unnatural-parity channel in nuclei are investigated in terms of the random-phase approximation. The particle-hole residual interaction consists of the ..pi.. and rho(2..pi..) meson-exchange attractive components in addition to the short-range repulsive Landau term. It is found that the nonresonant part of the iterated two-pion exchange moves the characteristics of the nuclear phase transition closer to those for rho meson condensation. This mode may dominate at high density.

9 citations


Journal ArticleDOI
TL;DR: In this paper, the autocorrelation function of the electric field is described using the techniques of Fourier analysis and the resulting equations possess the necessary conservation properties, but comprise new terms which hitherto have been lost in the conventional derivations.
Abstract: The system of quasi‐linear equations is derived without making use of the random phase approximation. The fluctuation quantities are described by the autocorrelation function of the electric field using the techniques of Fourier analysis. The resulting equations possess the necessary conservation properties, but comprise new terms which hitherto have been lost in the conventional derivations.

7 citations


Journal ArticleDOI
TL;DR: In this article, the general form of nuclear Hamiltonian equation of motion is derived within the Random Phase Approximation (RPA), and the connection between the Goldstone modes of motion (spurious states) and the equations of motion are shown.
Abstract: The general form of nuclear Hamiltonian equation of motion is derived within the Random Phase Approximation (RPA). The connection between the Goldstone modes of motion (spurious states) and the equations of motion is shown. The general method of extraction of spurious states from the solution of the RPA equations of motion is proposed.

7 citations


Journal ArticleDOI
TL;DR: In this paper, a self-consistent many-body theory for the standard basis operator Green's functions and an exact Dyson-type matrix equation for the interacting many-level systems was proposed.
Abstract: We propose a self-consistent many-body theory for the standard basis operator Green's functions and obtain an exact Dyson-type matrix equation for the interacting many-level systems. A zeroth order approximation, which neglects all the damping effects, is investigated in detail for the anisotropic Heisenberg model, the isotropic quadrupolar system and the Hubbard model. In the case of the anisotropic Heisenberg ferromagnet with both exchange and single-ion anisotropy the low-temperature renormalization of the spin-waves for the uniaxial ordering agrees with the Bloch-Dyson theory. For the spin-1 easy-plane ferromagnet, the critical parameters for the phase transition at zero temperature are determined and compared with other theories. The elementary excitation spectrum of the spin-1 isotropic quadrupolar system is calculated and compared with the random phase approximation and Callen-like decoupling schemes. Finally, the theory is applied to the study of the single-particle excitation spectrum of the Hubbard model.

Journal ArticleDOI
TL;DR: In this article, the authors used the function diagrammatic technique to investigate a model ferromagnet in the case, when the effective spin at a site is compounded of two anisotropically interacting electron spins, and the results are: the transverse magnetic excitations (Δm = ± 1) and the longitudinal ones ( Δm = 0) are obtained in the random phase approximation, magnetization and critical temperature are calculated to the first order in 1/z (the reciprocal of the effective number of ions interacting with a given ion).
Abstract: Green's function diagrammatic technique is used to investigate a model ferromagnet in the case, when the effective spin at a site is compounded of two anisotropically interacting electron spins. The results are: the transverse magnetic excitations (Δm = ± 1) and the longitudinal ones (Δm = 0) are obtained in the random phase approximation, magnetization and critical temperature are calculated to the first order in 1/z (the reciprocal of the effective number of ions interacting with a given ion), and exchange interaction at the same site gives the contrary effects in changes of the magnitudes mentioned above in dependence on the exchange-isotropy parameter I and the exchange-anisotropy parameter D. [Russian Text Ignored].

Journal ArticleDOI
TL;DR: In this article, the spin-flop paramagnetic phase transition of the Heisenberg antiferromagnet in the limit of zero anisotropy is studied by a Green function theory in the random phase approximation for S = 1/2 and by a spin wave theory including spin wave interactions for general spin.
Abstract: The spin-flop paramagnetic phase transition of the Heisenberg antiferromagnet in the limit of zero anisotropy is studied by a Green function theory in the random phase approximation for S =1/2 and by a spin wave theory including spin wave interactions for general spin. The phase transition is found to be of first order at finite temperature and the angle θ between the spins and the direction of applied field changes discontinuously at the transition. The spin wave theory predicts a non-zero excitation energy gap in the limit of zero anisotropy in the spin-flop phase.

Journal ArticleDOI
TL;DR: In this paper, a mean field approach and random phase approximation was used to obtain the equilibrium properties of the superradiant phase with infinite number of modes of radiation field and without trancation to a single rotating field, which is shown to be exact in the limit of large n.
Abstract: The thermodynamics and electrodynamics of the superradiant phase are analyzed on the basis of the Emeljanov·Klimontovich model by means of a mean field approach and random phase approximation. The model considers infinite modes of radiation field. The superradiant phase is characterized by a static and homogeneous Bose condensation of the transverse collective mode with zero wave vector. The thermodynamic Quantities and the dispersion relations for the collective mode are obtained in closed forms. While the thermodynamic properties of the present model are the same as those of the Dicke model, the electrodynamics differs in form from the latter. A softening of the lower branch of the collective mode behaves as (T- Te)l/2 for T> Te, whereas for T< Te it obeys a law Te- T or (Tc- T)I/2 according to the different regions of temperature and the polarizations. A light velocity is renormalized with an anisotropic constant. Properties of a system of n identical atoms with two levels interacting with a radiation field are now widely investigated. In the most of the works a simplification that takes account of only a single rotating field has been made. Within this simplified model it is shown that a mean field treatment is sufficient to obtain the equilibrium properties, which is shown to be exact in the limit of large n. I)~6) It was predicted that if the coupling between the two subsystems- the atoms and the radiation field-is sufficiently strong, the system exhibits a phase transition to an ordered state called a superradiant phase. In spite of this success, however, up to the present time a natural problem of infinite number of modes of the radiation field and without trancation to a single rotating field has been remained less clear. Emeljanov and Klimontovich 8

Journal ArticleDOI
TL;DR: In this article, the imaginary optical potentials for proton and neutron scattering have been calculated for /sup 40/Ca using random phase approximation transition densities to describe intermediate states, both inelastic and charge exchange intermediate states are considered.
Abstract: The imaginary optical potentials for proton and neutron scattering have been calculated for /sup 40/Ca using random phase approximation transition densities to describe intermediate states. Both inelastic and charge-exchange intermediate states are considered. The protons propagate in a nuclear-plus-Coulomb potential, and Coulomb excitation is included both for direct and exchange terms in the scattering amplitudes. Differences in the calculated neutron and proton optical potentials due to Coulomb excitation and isospin impurity of the random phase approximation states are found to be small. The expected exclusion of high-lying intermediate states by the Coulomb potential is present but it is compensated by a larger proton wave function in positive kinetic energy regions and by a more favorable local equivalent potential for protons.

Journal ArticleDOI
TL;DR: In this article, a variant of the RPA formalism for a mixed state is proposed, which permits simultaneous coupled approximations for the states of the mixture, and within this approximation an evaluation of the second-order properties of the excited states is possible.

Journal ArticleDOI
TL;DR: In this article, the influence of inner shells upon the anisotropy parameter of the 4p-photoelectrons angular distribution in Kr is investigated in the frame of the random phase approximation with exchange (RPAE).

Journal ArticleDOI
TL;DR: In this paper, a method was developed that allows effective calculation of local field effects on optical properties of non-cubic crystals in the Random Phase Approximation, expanding electron wave-functions on localized orbitals.

Journal ArticleDOI
TL;DR: In this paper, a new method is proposed for the calculation of the long wavelength part of the magnon dispersion curves of itinerant magnetic systems, which is the exact analog of the rigid muffin-tin approximation for the phonon frequencies in transition metals.

Journal ArticleDOI
TL;DR: In this paper, the random phase approximation in relation to the energy weighted maximum overlap model was examined for the first row hydride molecules, and a way of accounting for singlet-triplet splittings in particle-hole spectra was proposed.
Abstract: Examination of the random phase approximation in relation to the energy weighted maximum overlap model suggests a way of accounting for singlet–triplet splittings in particle–hole spectra. Calculations for the first row hydride molecules are used to illustrate applications.


Journal ArticleDOI
TL;DR: In this paper, the authors derived the dynamical susceptibilities for all temperatures within a one-band Hubbard model in the presence of dilute random impurities within the random phase approximation.
Abstract: The dynamical susceptibilities are derived for all temperatures within a one-band Hubbard model in the presence of dilute random impurities within the random phase approximation. Explicit expressions are obtained for the transverse susceptibility, spin-wave velocity and damping for T=0. The spin-wave velocity decreases linearly at first and then drastically at higher concentrations.

Journal ArticleDOI
TL;DR: In this article, the renormalized random phase approximation is derived from the perturbative Green's function approach via the Bethe-Salpeter equation and relations to the original derivation by the equations-of-motion method are discussed.

Book ChapterDOI
01 Jan 1981
TL;DR: In this article, a unified description of the nuclear ground and excited states based on the self consistent mean field approach is presented, and typical results on spherical and deformed nuclei, ranging from static properties to the effect of dynamical correlations are given.
Abstract: We present a unified description of the nuclear ground and excited states based on the self consistent mean field approach. Typical results on spherical and deformed nuclei, ranging from static properties to the effect of dynamical correlations are given. The success of the theory used in the interpretation of the nuclear structure seems to guarantee it usefulness as a predictive tool.

Journal ArticleDOI
TL;DR: In this article, four approximations for the intensity distribution of diffuse wave scattering by ordered phases are presented for the purpose of analyzing the intensity distributions of elastic wave scattering experiments, in order to extract the values of the mixing energies of ordered phases from the diffuse intensity distributions.
Abstract: Four approximations are presented for the purpose of analysing the intensity distribution of diffuse wave scattering by ordered phases. They are, in order of accuracy and mathematical complexity random phase approximation, Bethe-Peierls approximation, mean spherical approximation and improved mean spherical approximation. The third one is shown to be intimately related to, yet better than, the widely applied linearised approximation of Clapp and Moss (1966). The present theory is expected to be useful for extracting the values of the mixing energies of ordered phases from the diffuse intensity distributions of elastic wave scattering experiments.

Book ChapterDOI
01 Jan 1981
TL;DR: In this article, the effects of the range and anisotropy of the interaction on the critical dynamics of the longitudinal relaxation shape function of the transverse Ising model are investigated based on the resolution of kinetic equations for the correlation functions derived beyond the random phase approximation.
Abstract: The effects of the range and anisotropy of the interaction on the critical dynamics of the longitudinal relaxation shape function of the transverse Ising model are investigated. Our investigation is based on the resolution of kinetic equations for the correlation functions derived beyond the random phase approximation. We complete previous work by considering a very general interaction made of dipole-dipole, anistropic nearest-neighbour and isotropic infinite range contributions. It is shown that the overwhelming effects of range and anisotropy of the interaction are those of the dipolar part of the interaction.

Journal ArticleDOI
J. Krupski1
TL;DR: In this article, the inter and intraband static dielectric functions of degenerate zero-gap semiconductors placed in a magnetic field were calculated in the long wavelength limit using the random phase approximation and the Yafet wave functions.
Abstract: Using the random phase approximation and the Yafet wave functions the inter and intraband static dielectric functions of degenerate zero-gap semiconductors placed in a magnetic field are calculated in the long wavelength limit.

Journal ArticleDOI
TL;DR: In this article, the magnetoconductivity tensor σij of a two-dimensional (layer fo semiconductor plasma) was examined in the quantum strong field limit, such that electrons populate only the lowest Landau eigenstate with the magnetic field perpendicular to the 2D layer.
Abstract: The magnetoconductivity tensor σij of a two-dimensional (layer fo semiconductor plasma is examined here used high magnetic field conditions. The quantum strong field limit is considered, such that electrons populate only the lowest Landau eigenstate with the magnetic field perpendicular to the 2D layer. This work is based on a random phase approximation analysis of the 2D magnetoconductivity tensor previously set forth [1, 2], from which a highly tractable form for σij is developed in high magnetic fields. A closed form evaluation of the integral representation of the 2D layer magnetoconductivity tensor is carried out here, and the results are exceptionally simple in representing the full range of dynamic and nonlocal electromagnetic response. The final results for σij in the quantum strong field limit are expressed in terms of Incomplete Gamma Functions γ(x, −λ) in closed form, where x = Ωωc (ratio of frequency to cyclotron frequency) and λ = hk22mωc (nonlocality parameter).

Journal ArticleDOI
TL;DR: In this article, the inelastic collision of fast electrons with ground state closed shell atoms is investigated within the context of First Born Approximation and Random Phase Approximate.
Abstract: The inelastic collision of fast electrons with ground state closed shell atoms is investigated within the context of First Born Approximation and Random Phase Approximation. Generalized oscillator strengths and total cross sections for 11 S → n 1 D transitions in He and 11 S → n 1 S in Be are evaluated and discussed.

Book ChapterDOI
01 Jan 1981
TL;DR: In this paper, the interaction of electrons and lattice vibrations in polar materials was investigated taking into account their dielectric properties by using the microscopic dielectrics function, and the interaction between the electrons and the lattice vibration was investigated.
Abstract: The interaction of electrons and lattice vibrations in polar materials is investigated taking into account their dielectric properties by using the microscopic dielectric function, \( {\varepsilon _{\vec G\vec G}},\left( {\vec q} \right). \).