Showing papers on "Random phase approximation published in 1982"
TL;DR: In this paper, the frequency and wave-vector dependent macroscopic dielectric function eM(q, ω), which determines the energy loss function and in the limit q → 0 the optical properties, is calculated from the microscopic dielectrics matrix in the random phase approximation.
Abstract: In this review article, the frequency and wave-vector dependent macroscopic dielectric function eM(q, ω), which determines the energy loss function and in the limit q →0 the optical properties, is calculated from the microscopic dielectric matrix in the random phase approximation. The effect of the crystal potential is included by second order perturbation theory within the nearly free electron pseudopotential theory. The theory is applied to investigate the influence of periodic potential on the plasmon lineshape in simple metals and in semiconductors and comparison is made with experiment. In an attempt to explain remaining discrepancies between theory and experiment, various other effects are investigated based mostly on theories in the literature. These effects arise from many-body effects beyond the RPA, from the presence of phonons and from the polarizable core electrons.
120 citations
TL;DR: In this paper, the interaction of three nonlinearly coupled drift waves is investigated for the occurrence of stochastization of the phases and the applicability of the random phase approximation.
Abstract: The interaction of three nonlinearly coupled drift waves is investigated for the occurrence of stochastization of the phases and the applicability of the random phase approximation. The drift wave nonlinearities include the E×B and polarization drift couplings for waves that are linearly unstable for appropriate values of the perpendicular wavenumber. The conservation properties and sample numerical solutions for the exact three wave interaction are given along with the conservation properties and solutions of the corresponding random phase approximation equations.
108 citations
TL;DR: In this article, the Random Phase Approximation is used to discuss giant resonances and Sum Rules are considered in detail (AIP), and the AIP is applied to the giant resonance problem.
Abstract: The Random Phase Approximation is used to discuss giant resonances Sum Rules are considered in detail (AIP)
82 citations
TL;DR: In this paper, the dielectric response of the metal was obtained by using the random phase approximation for a jellium model with a surface represented by an infinite barrier, including the role of spatial dispersion (nonlocal response) and of the fact that the response varies continuously across the interface, which removed the divergence given by the phenomenological electrodynamics.
Abstract: We compute the electromagnetic field generated by an oscillating dipole located near a metal surface. The dielectric response of the metal is obtained by using the random phase approximation for a jellium model with a surface represented by an infinite barrier. The model includes the role of spatial dispersion (nonlocal response) and of the fact that the dielectric response varies continuously across the interface. These two effects remove the divergence given by the phenomenological electrodynamics (image formula).
49 citations
TL;DR: In this article, the relativistic random-phase approximation is generalized to describe excitations of an atomic system having a multiconfiguration ground state, and the response of such an atom to an imposed harmonic perturbation is determined by applying the time-dependent variational principle to a multi-figuration wave function constructed from Dirac orbitals.
Abstract: The relativistic random-phase approximation is generalized to describe excitations of an atomic system having a multiconfiguration ground state. The response of such an atom to an imposed harmonic perturbation is determined by applying the time-dependent variational principle to a multiconfiguration wave function constructed from Dirac orbitals. Terms in the wave function independent of the external field lead to the multiconfiguration Dirac-Fock description of the ground state. Terms proportional to the external field lead to a multiconfiguration generalization of the relativistic random-phase approximation. For the special case of an atom having a ground state with two electrons coupled to $J=0$ outside of closed shells, we write out in detail equations for the configuration weights and for the electronic orbitals. These equations are expanded in a suitable basis to give expressions for the excitation probabilities. An angular momentum analysis is carried out leading to a set of coupled algebraic equations for the configuration weights and a set of radial differential equations for the electronic orbitals.
41 citations
TL;DR: In this paper, the electromagnetic fields generated at a vacuum-metal interface by incident radiation were computed using a jellium model and the random phase approximation, and the validity of the Fresnel equations at small distances from the surface was discussed.
Abstract: We compute the electromagnetic fields generated at a vacuum–metal interface by incident radiation. We use a jellium model and the random phase approximation. The validity of the Fresnel equations at small distances from the surface is discussed. Numerical values for the continuous variation of the electric field vector through the interface are presented. Our main concern here is to illustrate the effects of the nonlocality of the dielectric response and of the continuous variation of the response function across the interface on the electrodynamic properties of the system.
34 citations
TL;DR: In this article, the total and the differential cross section for the elastic scattering of electrons on argon is calculated for energies below the ionization threshold, and the correlation corrections to them are found by solving the integral equation for the reducible self-energy part of the one-particle Green's function.
Abstract: The total and the differential cross section for the elastic scattering of electrons on argon is calculated for energies below the ionization threshold. The phase shifts were evaluated initially in the frozen-core Hartree-Fock approximation. The correlation corrections to them are found by solving the integral equation for the reducible self-energy part of the one-particle Green's function; this procedure is equivalent to solving the Schroedinger equation with the optical potential. The optical potential, being equal to the self-energy part of the one-particle Green's function, is found using many-body perturbation theory. Presented are the results of calculations for s, p, d, and f phase shifts and for the differential and the total cross sections. Comparison is made with other calculations and experimental data, and a good agreement is obtained.
32 citations
TL;DR: In this paper, the relativistic excitation energies and transition rates from the ground states to the first /sup 3/P/sub 1/ and /sup 1/S/sub 0/ excited states of beryllium-like ions are determined using the newly developed multiconfiguration relativistically random-phase approximation.
Abstract: Relativistic excitation energies and transition rates from the /sup 1/S/sub 0/ ground states to the first /sup 3/P/sub 1/ and /sup 1/P/sub 1/ excited states of berylliumlike ions are determined using the newly developed multiconfiguration relativistic random-phase approximation. Results from the multiconfiguration relativistic random-phase approximation theory are compared with those from other theories and experiments. The large discrepancies between the single-configuration relativistic random-phase approximation predictions of excitation energies and precise experimental values are resolved.
26 citations
TL;DR: In this paper, an alternative method for solving the Landau equations is presented, which allows analytical expressions for the response function, the odd sum rules and the strength of the modes, and the results obtained with the Skyrme forces are tested against the antisymmetry property of the forward particle-hole scattering amplitude on the Fermi surface.
24 citations
TL;DR: In this article, a critical evaluation of the optimized cluster theory, the optimized random phase approximation and the mean spherical model for describing the effect of attractive forces upon the structure and thermodynamics of liquids is given at the example of the square-well fluid with a variable range of the attractive interaction.
Abstract: A critical evaluation of the optimized cluster theory, the optimized random phase approximation and the mean spherical model for describing the effect of attractive forces upon the structure and thermodynamics of liquids is given at the example of the square-well fluid with a variable range of the attractive interaction. Our results demonstrate that for a general width of the attractive well, the optimized cluster theory is more accurate than the mean spherical model.
23 citations
TL;DR: In this article, the Hartree-Fock (HF) approximation is used to model the atomic wave function as an antisymmetrized product of one-electron wave functions.
Abstract: Publisher Summary The interaction of the electromagnetic field with atoms is not only a widespread natural process but also a convenient and effective method for studying their structure. The field weakly perturbs the atom and photoionization cross section permits one to obtain information on atomic wave function in the ground and excited states. The atomic electron structure and the motion and interaction of electrons determine the wave function and therefore the photoionization cross section. Each electron moves in the atom almost independently in some average, the so-called self-consistent field created by nuclei and all other electrons. The Hartree–Fock (HF) approximation presents the atomic wave function as an antisymmetrized product of one-electron wave functions. This chapter consciously understates the correlation role, considering as collective or correlational only those effects that cannot be described in one-electron approximation with any choice of self-consistent field. The chapter focuses on double-electron photoionization and one-electron photoionization process with special emphasis on one-electron photoionization to demonstrate that the corrections to one-electron picture due to direct interaction are very large. Some of many-electron effects beyond random phase approximation with exchange (RPAE) frame are also discussed in this chapter.
TL;DR: In this paper, the asymmetry parameter of the 3p photoelectrons in the region of 3s -1 4p resonance in argon is calculated and it is demonstrated that going beyond the random phase approximation frame by inclusion of the two-electron-two-hole excitation gives results which are in good agreement with experiment.
TL;DR: In this article, an extended version of the random phase approximation developed by Gaskell has been used to determine a good pair-potential by combining experimental results and molecular dynamics calculations.
Abstract: Accurate neutron diffraction measurements of the static structure factor S(Q) for small wave-vector transfers Q have been used to obtain the ‘coarse’ structure of the long-range part of the effective inter-particle potential in liquid aluminium, lead and bismuth. An extended version of the random phase approximation developed by Gaskell has been used. It is found that for Al and Pb the potential is of simple oscillatory nature while for Bi it is of ledge type. Finer details of the shape of the potential could not be evaluated. Methods to determine a good pair-potential by combining experimental results and molecular dynamics calculations are suggested.
TL;DR: In this article, the authors proposed an optimized random phase approximation (ORPA) approach to calculate the liquid structure factor of the alkali metals, and provided a first-order solution for such an approach.
Abstract: In a previous publication1 we have shown that the model of the one-component classical plasma on an inert background (OCP) provides a basis for calculating the liquid structure factor of the alkali metals. This was achieved by allowing the conduction electrons to screen the structure of the OCP through the formalism of linear screening theory, but an empirical cut-off of the screening correction at the first node of the electron-ion pseudpotential in wavenumber space was found to be necessary. The purpose of this letter is to stress that the above results point the way towards an unconventional optimized-random-phase-approximation (ORPA) approach2 to the structure of these liquid metals, and in fact provide already a good first-order solution for such an approach.
TL;DR: In this paper, the authors investigate dynamical susceptibilities associated with fluctuations of an amplitude and a phase of the incommensurate spin density wave of chromium using a model Hamiltonian within the framework of the random phase approximation.
Abstract: We investigate dynamical susceptibilities associated with fluctuations of an amplitude and a phase of the incommensurate spin density wave of chromium using a model Hamiltonian within the framework of the random phase approximation. They couple with charge density fluctuations with transfer momemtum q . The energy of the collective motion related to the amplitude fluctuation of the spin density wave (SDW) agrees with the energy gap of the single excitations in the limit q →0. The susceptibility related to the phase fluctuation has not a pole due to their coupling though the intensity of it has a peak and its peak height increases like q -2 with decreasing q .
TL;DR: In this paper, the magnetic excitation spectrum in HoCo2 was calculated using a combined model of localised moments on the holmium atoms and itinerant d electrons on the cobalt atoms.
Abstract: The magnetic excitation spectrum in HoCo2 is calculated using a combined model of localised moments on the holmium atoms and itinerant d electrons on the cobalt atoms The crystalline electric field acting on the holmium atoms is taken into account and the random phase approximation is used The calculated results of the magnetic excitation spectrum for HoCo2 at 6 and 18K are in fairly good agreement with recently observed inelastic neutron scattering measurements obtained by Castets et al (1982)
TL;DR: In this article, the procedure of solving equations for the generalized density matrix method is demonstrated in the Lipkin-Meshkov-Glick model, and self-consistency and adequacy of the basic equations of the method are shown.
TL;DR: In this article, the dispersion and damping of a collective mode of the acoustic kind in a degenerate electron-hole liquids was investigated and the implications of the results were discussed.
TL;DR: In this paper, a microscopic approach was used to derive a schematic Hamiltonian for studying the strengths and the energies of the three components of the dipole excitation, and explicit formulas within the random phase approximation accuracy were given for energies and strengths.
Abstract: We use a microscopic approach to derive a schematic Hamiltonian for studying the strengths and the energies of the three components (..delta..T/sub 3/ = +- 1,0) of the dipole excitation. Explicit formulas within the random phase approximation accuracy are given for energies and strengths. A significant isotensor contribution to the isospin splittings is found in agreement with recent experimental data.
TL;DR: In this paper, the stability condition of the cranked Hartree-Fock-Bogoliubov field is examined explicitly by solving the eigenvalue equation for the second order variation of the energy, which is reduced to an algebraic equation through a coupled dispersion formula.
Abstract: The stability condition of the cranked Hartree-Fock-Bogoliubov field is examined explicitly by solving the eigenvalue equation for the second order variation of the energy, which is reduced to an algebraic equation through a coupled dispersion formula. We confirm that the Hartree Fock-Bogoliubov field is unstable in the back bending region of an irregular rotational band, even though the frequency of the softest random phase approximation mode always has a positive value. We investigate properties of the softest mode in detail.
TL;DR: In this article, the structure functions of several liquid metals have been calculated using the equation developed by Andersen and Chandler through the so-called mode expansion, and a modified square-well potential with an attractive part inside the hard core has been taken as a perturbation over the hard sphere reference system.
TL;DR: In this article, the authors characterized volume oscillations of the nucleus which do not contribute to the photonuclear sum rule but show up as concentrated strength in, e.g., inelastic hadronic scattering.
Abstract: Compression modes are characterized as volume oscillations of the nucleus which do not contribute to the photonuclear sum rule but show up as concentrated strength in, e.g., inelastic hadronic scattering. Comparison of the nuclear response to different operators in the frame of a continuum random phase approximation is the theoretical technique used to search for such compression modes. Sharply concentrated strength is found only for the breathing mode and the isoscalar dipole mode. Large widths are expected for the isovector monopole, the isovector dipole compression mode, and the isoscalar quadrupole compression mode. For those modes whose escape width corresponds to a large fraction of the total width, one suggests the possibility of detecting them in coincidence experiments by observation of the decaying particle.
TL;DR: Dynamical correlation function of dynamical plane rotator model is expanded from the high temperature limit in this paper, which is also calculated by the random phase approximation at T > T c.
Abstract: Dynamical correlation function of dynamical plane rotator model is expanded from the high temperature limit. It is also calculated by the random phase approximation at T > T c .
01 Jan 1982
TL;DR: In this article, a simple extension of the Linear Response RPA model to spherical open-shell nuclei is described, which avoids the necessity to truncate the vector space and thus allows the inclusion of the entire continuum spectrum.
Abstract: We describe a simple extension of the Linear Response RPA model to spherical open-shell nuclei. The model allows replacing the uncorrelated p-h vacuum of the standard RPA by a correlated ground state wave function from preliminary model calculations. The model is exactly soluable in the sense that it avoids the necessity to truncate the vector space and thus allows the inclusion of the entire continuum spectrum.
TL;DR: In this paper, an approximation procedure is described to calculate the projected energies from an intrinsic rpa hf wave function, where the method of moments is used to find the relevant parameters.
Abstract: An approximation procedure is described to calculate the projected energies from an intrinsicrpa hf wave function. The method of moments is used to find the relevant parameters. A model calculation is carried out for illustrative purposes.
Journal Article•
TL;DR: In this paper, the authors investigate dynamical susceptibilities associated with fluctuations of an amplitude and a phase of the incommensurate spin density wave of chromium using a model Hamiltonian within the framework of the random phase approximation.
Abstract: We investigate dynamical susceptibilities associated with fluctuations of an amplitude and a phase of the incommensurate spin density wave of chromium using a model Hamiltonian within the framework of the random phase approximation. They couple with charge density fluctuations with transfer momemtum q . The energy of the collective motion related to the amplitude fluctuation of the spin density wave (SDW) agrees with the energy gap of the single excitations in the limit q →0. The susceptibility related to the phase fluctuation has not a pole due to their coupling though the intensity of it has a peak and its peak height increases like q -2 with decreasing q .