Showing papers on "Random phase approximation published in 1983"
TL;DR: In this paper, the authors derived a finite temperature linear response model for the giant dipole resonance in hot spherical nuclei, which is derived from the small amplitude limit of the FT-HFB-RPA.
85 citations
TL;DR: In this paper, the random-phase approximation integral equation for the density response function of the electron gas in a metal film is solved (in a cosine representation) for all wave vectors and frequencies.
Abstract: The random-phase-approximation integral equation for the density response function of the electron gas in a metal film is solved (in a cosine representation) for all wave vectors and frequencies. The Kohn-Sham-Lang ground-state wave functions are used in the computation of the noninteracting electron response. Numerical results are presented for the dynamic structure factor and for the screening field at the position of an oscillating point dipole placed in the surface region.
81 citations
TL;DR: In this article, the authors employ a localized orbital formulation in order to analyze the results in terms of local and charge-transfer excitations in the random phase approximation (RPA).
Abstract: The computational considerations involved in calculating ordinary and rotatory intensities and electronic excitation energies in the random phase approximation (RPA) are examined. We employ a localized orbital formulation in order to analyze the results in terms of local and charge-transfer excitations. Occupied orbitals are localized by the Foster–Boys procedure. The virtual space is transformed into a localized “valence” set that maximizes dipole strengths with the occupied counterparts, and a delocalized remainder. The two-electron integral transformation is performed with an efficient algorithm, based on Diercksen's, that generates only the particle–hole-type integrals required in the RPA. The lowest solutions of the RPA equations are obtained iteratively using a modification of the Davidson-Liu simultaneous vector expansion method. This allows the inclusion of the entire set of particle–hole states supported by a basis set of up to 102 orbitals. Calculations at this level give better excitation energies and intensities than SDCI methods, at substantial savings in computational effort. Comparative timings, computed results and analysis in terms of localized orbitals are given for planar and distorted ethylene using extended atomic orbital bases including diffuse functions. The results for planar ethylene are in excellent agreement with experiment.
70 citations
TL;DR: In this article, a theory of the small-q behavior of the static structure factor S(q) for monodisperse colloidal dispersions is presented in which the long-range forces between the colloid particles are treated in the random phase approximation.
Abstract: A theory of the small-q behaviour of the static structure factor S(q) for monodisperse colloidal dispersions is presented in which the long-range forces between the colloid particles are treated in the random phase approximation. By using a hard-sphere reference fluid, explicit results for the coefficients to (q4) in a small-q expansion of c(q), the Fourier transform of the direct correlation function, are obtained.The theory gives an expression for the osmotic compressibility of a dispersion that is equivalent to an empirical relation used to interpret light-scattering experiments on microemulsions. When applied to charge-stabilised dispersions the theory predicts the existence of a phase diagram closely analogous to one normally observed in molecular systems.
60 citations
TL;DR: In this paper, the wake of a swift charged particle in an electron gas using the full random phase-approximation dielectric function of this medium has been studied using the plasmon-pole approximation.
Abstract: A study has been made of the wake of a swift charged particle in an electron gas using the full random-phase-approximation dielectric function of this medium. Our earliest work using the plasmon-pole approximation to the dielectric function gives a good account of most aspects of the wake when the velocity of the particle is greater than the Fermi velocity.
45 citations
TL;DR: In this article, the level density and temperature dependence of collective states can be worked out explicitly in the special case of a schematic model for which the level densities and the temperature dependence can be explicitly worked out.
35 citations
TL;DR: In this article, the β-decay of both precursors is investigated by means of γ-ray, conversion electron and β-delayed neutron spectroscopy and the density of neutron-unbound levels in 95Sr and 97Sr has been derived from peak stripping analyses of the neutron spectra.
Abstract: Theβ-decay of 377 ms95Rb and 168ms97Rb has been thoroughly investigated by means ofγ-ray, conversion electron andβ-delayed neutron spectroscopy. More than 97% of theβ-decay to particle-bound states has been placed in level schemes of95Sr and97Sr. High-resolution neutron spectroscopic studies have allowed to extend the knowledge of the excitation spectra up to 9 MeV, respectively 10 MeV. The density of neutron-unbound levels in95Sr and97Sr has been derived from peak stripping analyses of the neutron spectra. Beta-strength functions (S
β(E)) have been investigated in detail. They indicate that Gamow-Tellerβ-decay of both precursors is dominated by nuclear structure. The discovered pronounced resonances and the variation in the shape ofS
β(E) are compared with predictions from the gross theory ofβ-decay and shell model calculations in the random phase approximation (RPA).
33 citations
TL;DR: In this paper, selfconsistency equations for the density relaxation and the longitudinal dynamical conductivity of the interacting Bose gas at temperature zero moving in a random potential were derived.
Abstract: We derive selfconsistency equations for the density relaxation and the longitudinal dynamical conductivity of the interacting Bose gas at temperature zero moving in a random potential. The equations describe a disorder-induced transition from a superfluid phase to an insulating phase, where the density is non-ergodic. The interaction of the bosons is treated in random phase approximation and the coupling to the impurities is calculated within generalized selfconsistent current relaxation theory. Scaling laws are discussed and explicit results are presented for the repulsive Bosgas with neutral impurities and for the charged Bose gas with charged impurities.
29 citations
29 citations
TL;DR: In this paper, the effects of zero-point motions of the surface due to random phase approximation vibrations were investigated and the main correction to the densities comes from low-lying collective states, whereas giant resonances are of minor importance.
Abstract: Fluctuations of the nuclear surface about the Hartree-Fock configuration can have a significant influence on ground state charge densities. We present simple formulas to describe the effects of zero-point motions of the surface due to random phase approximation vibrations. We use a collective treatment, justifying it with a solvable model. We find that the main correction to the densities comes from low-lying collective states, whereas giant resonances are of minor importance.
26 citations
TL;DR: In this paper, the frequency dependence of the dipole electric polarizability and electric shielding tensors of hydrogen and lithium nuclei in the LiH molecule was studied via some approximations to the polarization propagator method, i.e., STA, TDA, and RPA, allowing for dipole length, velocity, acceleration, and mixed formalisms.
Abstract: The frequency dependence of the dipole electric polarizability and electric shielding tensors of hydrogen and lithium nuclei in the LiH molecule has been studied via some approximations to the polarization propagator method, i.e., STA, TDA, and RPA, allowing for dipole length, velocity, acceleration, and mixed formalisms. The RPA nuclear electric shieldings are in a fairly good agreement with the corresponding experimental data, a discrepancy being observed for the parallel component at the Li nucleus.
01 Jan 1983
TL;DR: An overview of the current polarization proragator methods is presented in this article, which concentrates on the common properties of the polarization propagator approaches rather than describing the details of individual methods.
Abstract: An overview over the current polarization proragator methods is presented. These methods include the random phase approximation, the multi-configurational random phase approximation, the selfconsistent polarization propagator approximation, and the second order polarization propagator approximation. The paper concentrates on the common properties of the polarization propagator approaches rather than describing the details of the individual methods. It is thus intended as an introduction for the reader who is unfamiliar with polarization propagator methods.
TL;DR: In this paper, the static structure factor S(q) for a dispersion of charged colloidal particles is obtained for large values of the wavevector q by a model of the one component plasma (OCP), in which the direct correlation function c(r) is known analytically.
Abstract: The static structure factor S(q) for a dispersion of charged colloidal particles is obtained for large values of the wavevector q by a model of the one‐component plasma (OCP) in which the direct correlation function c(r) is known analytically. The model OCP is then used as a reference system for a perturbation theory of the small q behavior of the structure factor based upon a form of the random phase approximation suitably modified to treat the inclusion of a hard core in the perturbation potential. Explicit results are obtained for the coefficients in a small q expansion of the Fourier transform of the direct correlation function c(q). The values of S(q=0) determined from the extrapolation of the experimental data are analyzed in terms of the screened Coulomb interaction from the DLVO theory of colloid stability. The calculated surface potentials are found to be smaller than the values normally associated with this type of system. The theory gives the correct qualitative form for the small q region of S...
TL;DR: In this paper, a theory of spin waves in a sinusoidal phase is developed by considering δQ = Q - Qc as a small parameter relative to the closest commensurate wave vector Qc, for which the spin wave spectrum can be solved using sublattices and the random phase approximation.
Metz1
TL;DR: In this article, the pair potential of liquid metals shows damped oscillations at long range, and the structure factor in the random phase approximation is calculated using a form for this pair potential, proposed by Cummings.
TL;DR: In this paper, the authors show that the random phase approximation (RPA) is invariant to modifications in the virtual orbital potential, provided that all possible excitations within a given basis set are included.
Abstract: The use of modified virtual orbital potentials in perturbative polarization propagator approaches has been investigated. We find that the random‐phase approximation (RPA), which is identical to a first order polarization propagator approach, is invariant to modifications in the virtual orbital potential, provided that we include all possible excitations within a given basis set. Even in a moderately truncated excitation space we find only a small change in RPA. However, the second order polarization propagator approximation is not invariant to unitary transformations of the virtual orbitals. Certain denominator shifts in the correlation coefficients and in the two‐particle, two‐hole terms will reduce this dependence on the virtual orbital potential. Numerical applications to Be and CO show that we may have simple VN−1 potentials which do not give a convergent scheme. This happens when the virtual orbitall energies are too close to the orbital energies of the occupied orbitals.
01 Jan 1983
TL;DR: The most extensive calculations to date have employed either the random phase approximation with exchange (RPAE)1 or many-body perturbation theory (MBPT)2 as mentioned in this paper.
Abstract: In recent years considerable effort has been expended in the calculation of accurate atomic photoionization cross sections. Interestingly, it has proved necessary to proceed far beyond the simplest Hartree-Fock approximation (HFA) to achieve this goal. The most extensive calculations to date have employed either the random phase approximation with exchange (RPAE)1 or many-body perturbation theory (MBPT)2. Both of these approaches build systematically on standard Hartree-Fock theory and yield results which are generally in excellent agreement with experiment.
TL;DR: In this article, a more fundamental Hamiltonian was proposed in which the direct coupling between two modes is not assumed in contrast with the theory of Littlewood and Varma, and the collective modes assigned to new Raman peaks in 2H-NbSe 2.
Abstract: In the coexistent state of the charge (spin) density wave and superconductivity, mixed collective modes are formulated on the basis of a diagram method which corresponds to the random phase approximation. This theory gives the basis of the collective modes assigned to new Raman peaks in 2H–NbSe 2 . Our theory starts with a more fundamental Hamiltonian in which the direct coupling between two modes is not assumed in contrast with the theory of Littlewood and Varma.
TL;DR: In this article, the q and ω dependent dielectric function was examined in the random phase approximation for zinc-blende type, zero-gap semiconductors such as HgTe or HgSe.
Abstract: A theory of phonon dynamics of superconductors is presented on the basis of a Hamiltonian which includes the bare Coulomb interaction term and the bare ion frequency term. A diagram method which corresponds to the random phase approximation is adopted. This theory can provide a basis for discussions of anomalies of the phonon structure. In connection with anomalous aspects of phonon dynamics there exist several works in which anomalies directly reflect the singular behavior of the proper polarization function of the density fluctuation in the superconducting case. These works are criticized through our theory.
TL;DR: In this article, the strength function for deep-lying hole states in a nucleus is examined from a many-body point of view, and a formal theory of the strength and fragmentation of such states is developed by splitting the self-energy into background and doorway state contributions.
Abstract: The strength function for deep-lying hole states in a nucleus is examined from a many-body point of view. Due to their interaction with the compound state background, such single hole excitations are interpreted as quasihole states that are not eigenstates of the nuclear Hamiltonian. These states show up as giant resonances in the strength function, with position and width determined by the real and imaginary parts of the quasihole energy. A formal theory of the strength and fragmentation of such states is developed by splitting the self-energy into background and doorway state contributions. The theory is applied to the calculation of the strength function for the isotopes of Sn using doorway states of a collective nature that consist of a hole plus collective vibrations of the target nucleus. A microscopic description of both the collective excitations and the hole state that it dresses is given in terms of a modified random phase approximation procedure that uses Green's functions for the individual single particle and single hole states that have been dressed by their interaction with the nuclear background. Specific calculations for the isotopes of Sn show good agreement with experiment.
TL;DR: In this paper, it was shown that the expressions for the polarizability and intrinsic conductivity of a two-dimensional (2D) dense electron gas, obtained recently by Lee and Hong with the use of Mori formalism, can be derived more simply within the same scheme and that they are equivalent to the corresponding expressions in the random-phase approximation in the limit of small wave number.
Abstract: It is shown that the expressions for the polarizability and intrinsic conductivity of a two-dimensional (2D) dense electron gas, obtained recently by Lee and Hong with the use of Mori formalism, can be derived more simply within the same scheme and that they are equivalent to the corresponding expressions in the random-phase approximation in the limit of small wave number, i.e., $k\ensuremath{\rightarrow}0$ with $\frac{\ensuremath{\omega}}{k}$ finite. Similar expressions have been derived for the three-dimensional and one-dimensional electron gas. In the former the behavior of the intrinsic conductivity is similar to that in the 2D case, whereas in the latter it is very different.
TL;DR: In this paper, the self-energy operator of an electron liquid is examined by including the particle-hole and particle-particle ladder types of vertex corrections to the simplest approximation discussed by Hedin and Lundqvist.
TL;DR: In this article, the principal series approximation is extended to the description of two correlated quasiparticles states, enabling a treatment of these states that takes into account the coupling among the two particle Green's function and the particle-hole one.
Abstract: The principal series approximation is extended to the description of two correlated quasiparticles states, enabling a treatment of these states that takes into account the coupling among the two particle Green's function and the particle-hole one. This description is related to a random phase approximation treatment of collective states in open shell nuclei that includes simultaneously the particle-particle and particle-hole versions of the nuclear residual Hamiltonian. Using separable interactions it is found that the inclusion of the particle-particle part of the Hamiltonians greatly changes the properties of the 2/sup +/ states in the Sn isotopes.
TL;DR: In this paper, the anomalous temperature dependence of an elastic constant c 11 in antiferromagnetic metals, such as fcc Mn alloys, was studied by using the extended random phase approximation including the exchange interaction.
Abstract: The anomalous temperature dependence of an elastic constant c 11 in antiferromagnetic metals, say fcc Mn alloys, is studied. The c 11 is generally written in terms of a wave-vector dependent electron density susceptibility. This susceptibility in an itinerant-electron antiferromagnet may be calculated by using the extended random phase approximation including the exchange interaction. By numerical calculations in the tight-binding single band approximation, it is shown that c 11 decreases with increasing energy gap caused by the antiferromagnetic spin ordering both in fcc and bcc lattices. Especially for an fcc antiferromagnet with relatively large e / a ratio, there exists a certain critical value of the energy gap where c 11 becomes zero as the temperature is reduced from the Neel temperature T N . For a bcc antiferromagnet, there appears a remarkable gap of c 11 at T N . In such an anomalous behaviour of c 11 the exchange interaction between the itinerant electrons plays a particularly important role.
TL;DR: In this article, the authors studied the variational properties of the action functional appeared in the time-dependent Hartree-Bogoli theory and derived the equation for the quasi· particle random phase approximation (RPA) describing the collective excitation around certain static HB fields.
Abstract: We study the variational properties of the action functional appeared in the time-dependent Hartree·Bogoli1.lbov (TDHB) theory. Through the calculus of the second variation on the coset manifold SO(2N)/U(N), the Jacobi equation is obtained. Assuming the periodic Jacobi field, we derive in a natural way the equation for the quasi· particle random phase approximation (RPA) describing the collective excitation around certain static HB fields. The present method of obtaining the SO(2N) RPA may be useful to getthe SO(2N+1) RPA.
01 Jan 1983
TL;DR: In this paper, the Coulomb potential between any pair of particles is not just the pure 1/r potential discovered by Coulomb, but is strongly modified, usually being reduced.
Abstract: One of the major efforts involved in studying many particle systems is the discovery of the effective force between the particles. In atomic and condensed matter physics the underlying force is the Coulomb potential. Due to the presence of many particles simultaneously interacting the net potential between any pair of particles is never just the pure 1/r potential discovered by Coulomb, but is strongly modified, usually being reduced. This phenomenon is called screening. Let us begin with a classical example which is easily described. We shall see that even here there are surprises.
TL;DR: In this article, the perturbation theory of Weeks, Chandler and Anderson (WCA) has been employed to calculate the free energy and compressibility factor of simple dense fluids characterised by a double Yukawa potential.
Abstract: The perturbation theory of Weeks, Chandler and Anderson (WCA) has been employed to calculate the free energy and compressibility factor of simple dense fluids characterised by a double Yukawa potential The structure factor has been calculated in the random phase approximation together with theWCA prescription for the division of the pair potential The calculated values are in excellent agreement with experimental results
TL;DR: In this article, closed analytical expressions for the structure factor of simple monatomic liquids have been obtained using the double Yukawa potential function in the random phase approximation (RPA) together with a closed analytical expression for the structural factor.
Abstract: Closed analytical expressions for the structure factor of simple monatomic liquids have been obtained using the double Yukawa potential function in the random phase approximation (RPA) together wit