Showing papers on "Random phase approximation published in 2008"
TL;DR: In this article, the equivalence between the random phase approximation (RPA) to the ground state correlation energy and a ring-diagram simplification of the coupled cluster doubles (CCD) equations was shown.
Abstract: We present an analytic proof demonstrating the equivalence between the random phase approximation (RPA) to the ground state correlation energy and a ring-diagram simplification of the coupled cluster doubles (CCD) equations. In the CCD framework, the RPA equations can be solved in O(N4) computational effort, where N is proportional to the number of basis functions.
272 citations
TL;DR: A physically appealing reformulation of the RPA correlation model is developed that substantially reduces its computational complexity and may become the long-sought robust and efficient zero order post-Kohn-Sham correlation model.
Abstract: The random phase approximation (RPA) to the density functional correlation energy systematically improves upon many limitations of present semilocal functionals, but was considered too computationally expensive for widespread use in the past. Here a physically appealing reformulation of the RPA correlation model is developed that substantially reduces its computational complexity. The density functional RPA correlation energy is shown to equal one-half times the difference of all RPA electronic excitation energies computed at full and first order coupling. Thus, the RPA correlation energy may be considered as a difference of electronic zero point vibrational energies, where each eigenmode corresponds to an electronic excitation. This surprisingly simple result is intimately related to plasma theories of electron correlation. Differences to electron pair correlation models underlying popular correlated wave function methods are discussed. The RPA correlation energy is further transformed into an explicit f...
257 citations
TL;DR: In this article, it was shown that the competition between the pairing and the neutron-proton particle-particle and particle-hole interactions causes contributions to the neutrinoless double-beta decay matrix element to nearly vanish at internucleon distances of more than 2 or 3 fermis.
Abstract: We show that, within the quasiparticle random phase approximation (QRPA) and the renormalized QRPA (RQRPA) based on the Bonn-CD nucleon-nucleon interaction, the competition between the pairing and the neutron-proton particle-particle and particle-hole interactions causes contributions to the neutrinoless double-beta decay matrix element to nearly vanish at internucleon distances of more than 2 or 3 fermis. As a result, the matrix element is more sensitive to short-range/high-momentum physics than one naively expects. We analyze various ways of treating that physics and quantify the uncertainty it produces in the matrix elements, with three different treatments of short-range correlations.
238 citations
TL;DR: In this article, the self-consistent relativistic quasiparticle random-phase approximation (RQRPA) is extended by the quasiphon-phonon coupling (QPC) model using the QTBA, which is formulated in terms of the Bethe-Salpeter equation (BSE) in the two-quasiparticles space.
Abstract: The self-consistent relativistic quasiparticle random-phase approximation (RQRPA) is extended by the quasiparticle-phonon coupling (QPC) model using the quasiparticle time blocking approximation (QTBA). The method is formulated in terms of the Bethe-Salpeter equation (BSE) in the two-quasiparticle space with an energy-dependent two-quasiparticle residual interaction. This equation is solved either in the basis of Dirac states forming the self-consistent solution of the ground state or in the momentum representation. Pairing correlations are treated within the Bardeen-Cooper-Schrieffer (BCS) model with a monopole-monopole interaction. The same NL3 set of the coupling constants generates the Dirac-Hartree-BCS single-quasiparticle spectrum, the static part of the residual two-quasiparticle interaction and the quasiparticle-phonon coupling amplitudes. A quantitative description of electric dipole excitations in the chain of tin isotopes ($Z=50$) with the mass numbers $A=100,106,114,116,120$, and 130 and in the chain of isotones with ($N=50$) $^{88}\mathrm{Sr}$, $^{90}\mathrm{Zr}$, $^{92}\mathrm{Mo}$ is performed within this framework. The RQRPA extended by the coupling to collective vibrations generates spectra with a multitude of $2q\ensuremath{\bigotimes}\mathrm{phonon}$ (two quasiparticles plus phonon) states providing a noticeable fragmentation of the giant dipole resonance as well as of the soft dipole mode (pygmy resonance) in the nuclei under investigation. The results obtained for the photo absorption cross sections and for the integrated contributions of the low-lying strength to the calculated dipole spectra agree very well with the available experimental data.
102 citations
TL;DR: In this paper, different scattering mechanisms in graphene are explored and conductivity is calculated within the Boltzmann transport theory, and the effect of ripples on the transport using a surface roughness model developed for semiconductor heterostructures.
Abstract: Different scattering mechanisms in graphene are explored and conductivity is calculated within the Boltzmann transport theory. We provide results for short-range scattering using the random phase approximation for electron screening, as well as analytical expressions for the dependence of conductivity on the dielectric constant of the substrate. We further examine the effect of ripples on the transport using a surface roughness model developed for semiconductor heterostructures. We find that close to the Dirac point, σ ∼ n β , where β = 1 , 0 ,- 2 for Coulomb, short-range and surface roughness, respectively; implying that Coulomb scattering dominates over both short-range and surface roughness scattering at low density.
95 citations
TL;DR: In this paper, the Wannier basis is used to construct the one-electron part of the model Hamiltonian for the low-energy LDA band, which can be used for the analysis of strongly correlated materials.
Abstract: The electronic and magnetic properties of many strongly correlated systems are controlled by a limited number of states, located near the Fermi level and well isolated from the rest of the spectrum. This opens a formal way for combining the methods of first-principles electronic structure calculations, based on the density-functional theory (DFT), with many-body models, formulated in the restricted Hilbert space of states close to the Fermi level. The core of this project is the so-called 'realistic modeling' or the construction of the many-body model Hamiltonian entirely from first principles. Such a construction should be able to go beyond the conventional local-density approximation (LDA), which typically supplements the density-functional theory, and incorporate the physics of Coulomb correlations. It should also provide a transparent physical picture for the low-energy properties of strongly correlated materials. In this review article, we will outline the basic ideas of such a realistic modeling, which consists of the following steps: (i)?the construction of the complete Wannier basis set for the low-energy LDA band; (ii)?the construction of the one-electron part of the model Hamiltonian in this Wannier basis; (iii)?the calculation of the screened Coulomb interactions for the low-energy bands by means of the constrained DFT. The most difficult part of this project is the evaluation of the screening caused by outer bands, which may have the same (e.g., the transition-metal 3d) character as the low-energy bands. The latter part can be efficiently done by combining the constrained DFT with the random-phase approximation?(RPA) for the screened Coulomb interaction. The entire procedure will be illustrated on a series of examples, including the distorted transition-metal perovskite oxides, compounds with the inversion-symmetry breaking caused by the defects, and the alkali hyperoxide KO2, which can be regarded as an analog of strongly correlated systems where the localized electrons reside on the molecular orbitals of the O2? dimer. In order to illustrate the abilities of the realistic modeling, we will also consider solutions of the low-energy models obtained for a number of systems, and argue that it can be used as a powerful tool for the exploration and understanding of the properties of strongly correlated materials.
84 citations
TL;DR: In this article, the Hartree-Fock-Bogoliubov equation in coordinate space with spherical symmetry has been studied in the context of pairing vibration analysis for low lying pairing modes and giant pairing vibrations.
Abstract: We study pairing vibrations in $^{18,20,22}$O and $^{42,44,46}$Ca nuclei solving the time-dependent Hartree-Fock-Bogoliubov equation in coordinate space with spherical symmetry. We use the SLy4 Skyrme functional in the normal part of the energy density functional and a local density dependent functional in its pairing part. Pairing vibrations are excited by two-neutron transfer operators. Strength distributions are obtained using the Fourier transform of the time-dependent response of two-neutron pair-transfer observables in the linear regime. Results are in overall agreement with quasiparticle random phase approximation calculations for Oxygen isotopes, though differences appear when increasing the neutron number. Both low lying pairing modes and giant pairing vibrations (GPV) are discussed. The GPV is observed in the Oxygen but not in the Calcium isotopes.
83 citations
TL;DR: In this paper, the authors describe the helical spin fluctuation induced by the Rashba-type anti-symmetric spin-orbit coupling and identify two stable superconducting phases with either the dominant p-wave ( s + P -wave) symmetry or the d-wave symmetry.
Abstract: Superconductivity and magnetism in the non-centrosymmetric heavy fermion compound CePt 3 Si and related materials are theoretically investigated. On the basis of the random phase approximation (RPA) analysis of the extended Hubbard model, we describe the helical spin fluctuation induced by the Rashba-type anti-symmetric spin–orbit coupling and identify two stable superconducting phases with either the dominant p -wave ( s + P -wave) symmetry or the d -wave ( p + D + f -wave) symmetry. The effect of the coexistent antiferromagnetic order is investigated in both states. The superconducting order parameter, quasiparticle density of state, NMR 1/ T 1 T , specific heat, anisotropy of H c2 , and possible multiple phase transitions are discussed in detail. A comparison with experimental results indicates that the s + P -wave superconducting state is likely realized in CePt 3 Si.
80 citations
TL;DR: An analytical summation of the infinite series of ladder diagrams which describe the excitonic effect finds that the ladder-type vertex corrections become crucial close to the threshold as the ratio of the nth order ladder term to the same order random phase approximation contribution is ln(n)|qv-omega|/N(n).
Abstract: Polarizability of noninteracting 2D Dirac electrons has a 1/square root(qv-omega) singularity at the boundary of electron-hole excitations. The screening of this singularity by long-range electron-electron interactions is usually treated within the random phase approximation. The latter is exact only in the limit of N-->infinity, where N is the "color" degeneracy. We find that the ladder-type vertex corrections become crucial close to the threshold as the ratio of the nth order ladder term to the same order random phase approximation contribution is ln(n)|qv-omega|/N(n). We perform an analytical summation of the infinite series of ladder diagrams which describe the excitonic effect. Beyond the threshold, qv>omega, the real part of the polarization operator is found to be positive leading to the appearance of a strong and narrow plasmon resonance.
76 citations
TL;DR: In this paper, the single-particle spectral function for the one-band Bose-Hubbard model within the random-phase approximation (RPA) was calculated, and the capability of the RPA to correctly account for quantum fluctuations in the vicinity of the QPT was discussed.
Abstract: We calculate the single-particle spectral function for the one-band Bose-Hubbard model within the random-phase approximation (RPA). In the strongly correlated superfluid, in addition to the gapless phonon excitations, we find extra gapped modes, which become particularly relevant near the superfluid-Mott quantum phase transition (QPT). The strength in one of the gapped modes, a precursor of the Mott phase, grows as the QPT is approached and evolves into a hole (particle) excitation in the Mott insulator depending on whether the chemical potential $\ensuremath{\mu}$ is above (below) the tip of the lobe. The sound velocity $c$ of the Goldstone modes remains finite when the transition is approached at constant density; otherwise, it vanishes at the transition. It agrees well with Bogoliubov theory except close to the transition. We also calculate the spatial correlations for bosons in an inhomogeneous trapping potential creating alternating shells of Mott insulator and superfluid. Finally, we discuss the capability of the RPA to correctly account for quantum fluctuations in the vicinity of the QPT.
67 citations
TL;DR: In this paper, a semi-analytical expression for the dynamical density-density linear response function of noninteracting massless Dirac fermions (the so-called Lindhard function) at finite temperature is presented.
Abstract: At low energies, electrons in doped graphene sheets are described by a massless Dirac fermion Hamiltonian. In this work we present a semi-analytical expression for the dynamical density-density linear-response function of noninteracting massless Dirac fermions (the so-called "Lindhard" function) at finite temperature. This result is crucial to describe finite-temperature screening of interacting massless Dirac fermions within the Random Phase Approximation. In particular, we use it to make quantitative predictions for the specific heat and the compressibility of doped graphene sheets. We find that, at low temperatures, the specific heat has the usual normal-Fermi-liquid linear-in-temperature behavior, with a slope that is solely controlled by the renormalized quasiparticle velocity.
TL;DR: In this paper, the neutrino-nucleus cross sections were calculated using a consistent relativistic mean field theoretical framework, where the weak lepton-hadron interaction was expressed in the standard current-current form and the nuclear ground state was described with the relativistically Hartree-Bogoliubov model.
Abstract: Inclusive neutrino-nucleus cross sections are calculated using a consistent relativistic mean-field theoretical framework. The weak lepton-hadron interaction is expressed in the standard current-current form, the nuclear ground state is described with the relativistic Hartree-Bogoliubov model, and the relevant transitions to excited nuclear states are calculated in the relativistic quasiparticle random-phase approximation. Illustrative test calculations are performed for charged-current neutrino reactions on 12C, 16O, 56Fe, and 208Pb, and results compared with previous studies and available data. Through the use of the experimental neutrino fluxes, the averaged cross sections are evaluated for nuclei of interest for neutrino detectors. We analyze the total neutrino-nucleus cross sections and the evolution of the contribution of the different multipole excitations as a function of neutrino energy. The cross sections for reactions of supernova neutrinos on 16O and 208Pb target nuclei are analyzed as functions of the temperature and chemical potential.
TL;DR: This well-established treatment of Thomson scattering on free electrons is generalized in the Born-Mermin approximation by including collisions and it is shown that, in the transition region from collective to noncollective scattering, the consideration of collisions is important.
Abstract: Collective Thomson scattering with extreme ultraviolet light or x rays is shown to allow for a robust measurement of the free electron density in dense plasmas. Collective excitations like plasmons appear as maxima in the scattering signal. Their frequency position can directly be related to the free electron density. The range of applicability of the standard Gross-Bohm dispersion relation and of an improved dispersion relation in comparison to calculations based on the dielectric function in random phase approximation is investigated. More important, this well-established treatment of Thomson scattering on free electrons is generalized in the Born-Mermin approximation by including collisions. We show that, in the transition region from collective to noncollective scattering, the consideration of collisions is important.
TL;DR: In this paper, an efficient pseudo-spectral numerical method is introduced for calculating a selfconsistent field (SCF) approximation for the linear susceptibility of ordered phases in block copolymer melts (sometimes referred to as the random phase approximation).
Abstract: An efficient pseudo-spectral numerical method is introduced for calculating a self-consistent field (SCF) approximation for the linear susceptibility of ordered phases in block copolymer melts (sometimes referred to as the random phase approximation). Our method is significantly more efficient than that used in the first calculations of this quantity by Shi and Laradji and co-workers, allowing for the study of more strongly segregated structures. We have re-examined the stability of several phases of diblock copolymer melts and find that some conclusions of Laradji et al. regarding the stability of the gyroid phase were the result of insufficient spatial resolution. We find that an epitaxial (k = 0) instability of the gyroid phase with respect to the hexagonal phase that was considered previously by Matsen competes extremely closely with an instability that occurs at a nonzero crystal wavevector k.
TL;DR: In this article, a new framework of the deformed quasiparticle-random-phase approximation (QRPA) was developed where the Skyrme density functional and the density-dependent pairing functional were consistently treated.
Abstract: We develop a new framework of the deformed quasiparticle-random-phase approximation (QRPA) where the Skyrme density functional and the density-dependent pairing functional are consistently treated. Numerical applications are carried out for the isovector dipole and the isoscalar quadrupole modes in the spherical {sup 20}O and in the deformed {sup 26}Ne nuclei, and the effect of the momentum-dependent terms of the Skyrme effective interaction for the energy-weighted sum rule is discussed. As a further application, we present for the first time the moments of inertia of {sup 34}Mg and {sup 36}Mg using the Thouless-Valatin procedure based on the self-consistent deformed QRPA, and we show the applicability of our new calculation scheme not only for the vibrational modes but also for the rotational modes in deformed neutron-rich nuclei.
TL;DR: In this article, the variances and covariances associated to the nuclear matrix elements (NME) of neutrinoless double beta decay are estimated within the quasiparticle random phase approximation (QRPA).
Abstract: The variances and covariances associated to the nuclear matrix elements (NME) of neutrinoless double beta decay are estimated within the quasiparticle random phase approximation (QRPA). It is shown that correlated NME uncertainties play an important role in the comparison of neutrinoless double beta decay rates for different nuclei, and that they are degenerate with the uncertainty in the reconstructed Majorana neutrino mass.
TL;DR: Theoretical {beta}-delayed-neutron spectra are calculated based on the Quasiparticle Random-Phase Approximation (QRPA) and the Hauser-Feshbach statistical model.
Abstract: Theoretical {beta}-delayed-neutron spectra are calculated based on the Quasiparticle Random-Phase Approximation (QRPA) and the Hauser-Feshbach statistical model. Neutron emissions from an excited daughter nucleus after {beta} decay to the granddaughter residual are more accurately calculated than in previous evaluations, including all the microscopic nuclear structure information, such as a Gamow-Teller strength distribution and discrete states in the granddaughter. The calculated delayed-neutron spectra agree reasonably well with those evaluations in the ENDF decay library, which are based on experimental data. The model was adopted to generate the delayed-neutron spectra for all 271 precursors.
TL;DR: In this article, the relativistic random-phase approximation (RRPA) was applied to axially deformed nuclei for the case of axial symmetry and nonlinear energy functionals and solved with the help of a new parallel code.
Abstract: Covariant density functional theory, in the framework of self-consistent relativistic mean field (RMF) and relativistic random-phase approximation (RRPA), is for the first time applied to axially deformed nuclei. The fully self-consistent RMF+RRPA equations are posed for the case of axial symmetry and nonlinear energy functionals and solved with the help of a new parallel code. Formal properties of RPA theory are studied and special care is taken to validate the proper decoupling of spurious modes and their influence on the physical response. Sample applications to the magnetic and electric dipole transitions in $^{20}\mathrm{Ne}$ are presented and analyzed.
TL;DR: In this article, the electronic states of the Fe 2 As 2 plane in iron-based superconductors are investigated on the basis of the two-dimensional 16-band d-p model which includes the Coulomb interaction on a Fe site.
Abstract: The electronic states of the Fe 2 As 2 plane in iron-based superconductors are investigated on the basis of the two-dimensional 16-band d – p model which includes the Coulomb interaction on a Fe site: the intra- and inter-orbital direct terms U and U ', the Hund's coupling J and the pair-transfer J '. Using the random phase approximation (RPA), we obtain the magnetic phase diagram including the stripe and the incommensurate order on the U '– J plane. We also solve the superconducting gap equation within the RPA and find that, for large J , the most favorable pairing symmetry is extended s -wave whose order parameter changes its sign between the hole pockets and the electron pockets, while it is d x y -wave for small J .
TL;DR: In this article, the effect of phonons and disorder due to charged impurities and unitary scatterers on the infrared conductivity of graphene at finite chemical potential and temperature was studied.
Abstract: We study the infrared conductivity of graphene at finite chemical potential and temperature taking into account the effect of phonons and disorder due to charged impurities and unitary scatterers, that is, considering all possible single-particle scattering mechanisms. The screening of the long-range Coulomb potential is treated using the random phase approximation coupled to the coherent potential approximation. The effect of the electron-phonon coupling is studied in second-order perturbation theory. The theory has essentially one free parameter, namely, the number of charge impurities per carbon, nCi. Our most important results are the finding of an anomalous enhancement of the conductivity in a frequency region that is blocked by Pauli exclusion, in a picture based on independent electrons, and an impurity broadening of the conductivity threshold, close to twice the chemical potential. We also find that phonons induce Stokes and anti-Stokes lines that produce an excess conductivity, when compared to the far infrared value of σ0=(π/2)e2/h.
TL;DR: In this article, the spin-flip strengths in photon scattering experiments with a quasi-monochromatic, linearly polarized photon beam were measured with uncertainties considerably smaller than those in a previous study, leading to a reexamination of the total strength.
Abstract: Spin-flip $M1$ strengths in $^{208}\mathrm{Pb}$ have been measured in photon scattering experiments with a quasi-monochromatic, linearly polarized photon beam. The data resolve an $M1$ giant resonance into at least seven, possibly eight, discrete transitions at excitation energies between 7.1 and 7.4 MeV below the neutron separation energy. The $M1$ strengths are measured with uncertainties considerably smaller than those in a previous study, which leads to a reexamination of the total strength. Experimental results are compared with an estimation of self-consistent random phase approximation using a semirealistic interaction.
TL;DR: In this article, the effect of phonons and disorder due to charged impurities and unitary scatterers on the infrared conductivity of graphene at finite chemical potential and temperature was studied.
Abstract: We study the infrared conductivity of graphene at finite chemical potential and temperature taking into account the effect of phonons and disorder due to charged impurities and unitary scatterers. The screening of the long-range Coulomb potential is treated using the random phase approximation coupled to the coherent potential approximation. The effect of the electron-phonon coupling is studied in second-order perturbation theory. The theory has essentially one free parameter, namely, the number of charge impurities per carbon, n^{{\rm C}}_i. We find an anomalous enhancement of the conductivity in a frequency region that is blocked by Pauli exclusion and an impurity broadening of the conductivity threshold. We also find that phonons induce Stokes and anti-Stokes lines that produce an excess conductivity, when compared to the far infrared value of \sigma_0 = (\pi/2) e^2/h.
TL;DR: In this article, the authors investigated the electronic states of the Fe2As2 plane in iron-based superconductors and obtained the magnetic phase diagram including the stripe and the incommensurate order on the U'-J plane.
Abstract: The electronic states of the Fe2As2 plane in iron-based superconductors are investigated on the basis of the two-dimensional 16-band d-p model which includes the Coulomb interaction on a Fe site: the intra- and inter-orbital direct terms U and U', the Hund's coupling J and the pair-transfer J'. Using the random phase approximation (RPA), we obtain the magnetic phase diagram including the stripe and the incommensurate order on the U'-J plane. We also solve the superconducting gap equation within the RPA and find that, for large J, the most favorable pairing symmetry is extended s-wave whose order parameter changes its sign between the hole pockets and the electron pockets, while it is dxy-wave for small J.
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TL;DR: In this paper, the authors systematically analyzed the low-lying strength of very neutron-rich spherical nuclei and found that the great neutron excess favors the appearance of a deformed ground state.
Abstract: The E1 strength is systematically analyzed in very neutron-rich Sn nuclei, beyond $^{132}$Sn until $^{166}$Sn, within the Relativistic Quasiparticle Random Phase Approximation. The great neutron excess favors the appearance of a deformed ground state for $^{142-162}$Sn. The evolution of the low-lying strength in deformed nuclei is determined by the interplay of two factors, isospin asymmetry and deformation: while greater neutron excess increases the total low-lying strength, deformation hinders and spreads it. Very neutron rich deformed nuclei may not be as good candidates as stable spherical nuclei like $^{132}$Sn for the experimental study of low-lying E1 strength.
TL;DR: In this article, the pairing symmetry of heavy fermion superconductors was studied under the conditions of antiferromagnetic spin fluctuations and it was shown that the gap function has line nodes on the Fermi surface and the resulting density of state in the superconducting state shows a similar character to that of usual d-wave superconductions.
Abstract: We study the pairing symmetry of the noncentrosymmetric heavy fermion superconductors CeRhSi 3 and CeIrSi 3 under pressures, which are both antiferromagnets at ambient pressure. We solve the Eliashberg equation by means of the random phase approximation and find that the mixed state of extended s - and p -wave rather than the d + f wave state could be realized by enhanced antiferromagnetic spin fluctuations. It is elucidated that the gap function has line nodes on the Fermi surface and the resulting density of state in the superconducting state shows a similar character to that of usual d -wave superconductors, resulting in the NMR relaxation rate 1/( T 1 T ) that exhibits no coherence peak and behaves like 1/( T 1 T )∝ T 2 at low temperatures.
TL;DR: In this paper, the Green's function was used to estimate the longitudinal susceptibility of the spin-1/2 low-dimensional Heisenberg ferromagnet in a magnetic field.
Abstract: Longitudinal susceptibility of the spin-1/2 low-dimensional Heisenberg ferromagnet in a magnetic field, is studied by the Green's function method within the random phase approximation. The static and dynamic longitudinal susceptibilities are calculated in the low- and high-field regions. Power laws for the position and height of the static susceptibility maximum are shown not to support the predictions of Landau theory.
TL;DR: Full configuration interaction data are used to quantify the accuracy of approximate adiabatic connection forms in describing two challenging problems in density functional theory--the singlet ground state potential energy curve of H(2) in a restricted formalism and the energies of the helium isoelectronic series.
Abstract: Full configuration interaction (FCI) data are used to quantify the accuracy of approximate adiabatic connection (AC) forms in describing two challenging problems in density functional theory—the singlet ground state potential energy curve of H2 in a restricted formalism and the energies of the helium isoelectronic series, H− to Ne8+. For H2, an exponential-based form yields a potential energy curve that is virtually indistinguishable from the FCI curve, eliminating the unphysical barrier to dissociation observed previously with a [1,1]-Pade-based form and with the random phase approximation. For the helium isoelectronic series, the Pade-based form gives the best overall description, followed by the exponential form, with errors that are orders of magnitude smaller than those from a standard hybrid functional. Particular attention is paid to the limiting behavior of the AC forms with increasing bond distance in H2 and increasing atomic number in the isoelectronic series; several forms describe both limits ...
TL;DR: In this paper, a detailed theoretical study of the electronic transport properties of monolayer graphene is presented, where the quantum and transport conductivities are calculated on the basis of the usual momentum-balance equation derived from a semiclassical Boltzmann equation.
Abstract: We present a detailed theoretical study of the electronic transport properties of monolayer graphene. The quantum and transport conductivities are calculated on the basis of the usual momentum-balance equation derived from a semiclassical Boltzmann equation. We investigate carrier-impurity scattering in a massless Dirac quasiparticle system. The carrier interactions with remote and background impurities are considered, and the carrier–carrier screening is included within the random phase approximation. The dependence of the conductivities on temperature is also examined. Moreover, a very simple analytical formula is proposed such that only one fitting parameter is needed in order to make a quantitative comparison with the experimental results.
TL;DR: An analytic proof demonstrating the equivalence between the random phase approximation to the ground state correlation energy and a ring-diagram simplification of the coupled cluster doubles (CCD) equations is presented.
Abstract: We present an analytic proof demonstrating the equivalence between the Random Phase Approximation (RPA) to the ground state correlation energy and a ring-diagram simplification of the Coupled Cluster Doubles (CCD) equations. In the CCD framework, the RPA equations can be solved in $\mathcal{O}(N^4)$ computational effort, where $N$ is proportional to the number of basis functions.
TL;DR: In this article, the current status of the incompressibility coefficient of symmetric nuclear matter is reviewed from experimental data on isoscalar giant monopole and dipole resonances (compression modes) in nuclei by employing the microscopic theory based on the Random Phase Approximation (RPA).
Abstract: Accurate assessment of the value of the incompressibility coefficient, K
∞, of symmetric nuclear matter, which is directly related to the curvature of the equation of state (EOS), is needed to extend our knowledge of the EOS in the vicinity of the saturation point. We review the current status of K
∞ as determined from experimental data on isoscalar giant monopole and dipole resonances (compression modes) in nuclei by employing the microscopic theory based on the Random Phase Approximation (RPA). The importance of full self-consistent calculations is emphasized. In recent years, a comparision between RPA calculations based on either non-relativistic effective interactions or relativistic Lagrangians has been pursued in great detail. It has been pointed out that these two types of models embed different ansatz for the density dependence of the symmetry energy. This fact has consequences on the extraction of the nuclear incompressibility, as it is discussed. The comparison with other ways of extracting K
∞ from experimental data is highlighted.