Showing papers on "Random phase approximation published in 2007"
TL;DR: In this paper, a theoretical study of electron mobility in cylindrical gated silicon nanowires at 300 K based on the Kubo-Greenwood formula and the self-consistent solution of the Schrodinger and Poisson equations is presented.
Abstract: We present a theoretical study of electron mobility in cylindrical gated silicon nanowires at 300 K based on the Kubo-Greenwood formula and the self-consistent solution of the Schrodinger and Poisson equations. A rigorous surface roughness scattering model is derived, which takes into account the roughness-induced fluctuation of the subband wave function, of the electron charge, and of the interface polarization charge. Dielectric screening of the scattering potential is modeled within the random phase approximation, wherein a generalized dielectric function for a multi-subband quasi-one-dimensional electron gas system is derived accounting for the presence of the gate electrode and the mismatch of the dielectric constant between the semiconductor and gate insulator. A nonparabolic correction method is also presented, which is applied to the calculation of the density of states, the matrix element of the scattering potential, and the generalized Lindhard function. The Coulomb scattering due to the fixed i...
322 citations
TL;DR: In this article, the charge distribution induced by external fields in finite stacks of graphene planes, or in semi-infinite graphite is considered, and the interlayer electronic hybridization is described by a nearest-neighbor hopping term.
Abstract: The charge distribution induced by external fields in finite stacks of graphene planes, or in semi-infinite graphite is considered. The interlayer electronic hybridization is described by a nearest-neighbor hopping term, and the charge induced by the self-consistent electrostatic potential is calculated within the linear response theory (random phase approximation). The screening properties are determined by contributions from interband and intraband electronic transitions. In neutral systems, only interband transitions contribute to the charge polarizability, leading to insulatinglike screening properties, and to oscillations in the induced charge, with a period equal to the interlayer spacing. In doped systems, we find a screening length that is equivalent to two-to-three graphene layers, superimposed to significant charge oscillations.
160 citations
TL;DR: In this paper, a method for solving the random-phase approximation (RPA) in the self-consistent Hartree-Fock (HF) and density-functional theory is proposed.
Abstract: We propose a practical method for solving the random-phase approximation (RPA) in the self-consistent Hartree-Fock (HF) and density-functional theory. The method is based on numerical evaluation of the residual interactions utilizing the finite amplitude of single-particle wave functions. The method only requires calculations of the single-particle Hamiltonian constructed with independent bra and ket states. Using the present method, the RPA calculation becomes possible with a little extension of a numerical code of the static HF calculation. We demonstrate the usefulness and accuracy of the present method by performing test calculations for isoscalar responses in deformed $^{20}\mathrm{Ne}$.
102 citations
TL;DR: Time-dependent Hartree-Fock (TD-HF) and time-dependent configuration interaction ( TD-CI) methods with Gaussian basis sets have been compared in modeling the response of hydrogen molecule, butadiene, and hexatriene exposed to very short, intense laser pulses, possibly signaling an approach to ionization.
Abstract: Time-dependent Hartree-Fock (TD-HF) and time-dependent configuration interaction (TD-CI) methods with Gaussian basis sets have been compared in modeling the response of hydrogen molecule, butadiene, and hexatriene exposed to very short, intense laser pulses (760nm, 3cycles). After the electric field of the pulse returns to zero, the molecular dipole continues to oscillate due to the coherent superposition of excited states resulting from the nonadiabatic excitation caused by the pulse. The Fourier transform of this residual dipole gives a measure of the nonadiabatic excitation. For low fields, only the lowest excited states are populated, and TD-CI simulations using singly excited states with and without perturbative corrections for double excitations [TD-CIS(D) and TD-CIS, respectively] are generally in good agreement with the TD-HF simulations. At higher field strengths, higher states are populated and the methods begin to differ significantly if the coefficients of the excited states become larger than ∼0.1. The response of individual excited states does not grow linearly with intensity because of excited state to excited state transitions. Beyond a threshold in the field strength, there is a rapid increase in the population of many higher excited states, possibly signaling an approach to ionization. However, without continuum functions, the present TD-HF and TD-CI calculations cannot model ionization directly. The TD-HF and TD-CIS simulations are in good accord because the excitation energies obtained by linear response TD-HF [also known as random phase approximation (RPA)] agree very well with those obtained from singly excited configuration interaction (CIS) calculations. Because CIS excitation energies with the perturbative doubles corrections [CIS(D)] are on average lower than the CIS excitation energies, the TD-CIS(D) response is generally stronger than TD-CIS.
101 citations
TL;DR: In this article, a model for the microscopic description of excited states of the even-even open-shell atomic nuclei is formulated which allows one to go beyond the quasiparticle random phase approximation.
Abstract: The problem of the microscopic description of excited states of the even-even open-shell atomic nuclei is considered. A model is formulated which allows one to go beyond the quasiparticle random phase approximation. The physical content of the model is determined by the quasiparticle time blocking approximation (QTBA) which enables one to include contributions of the two-quasiparticle and the two-phonon configurations, while excluding (blocking) more complicated intermediate states. In addition, the QTBA ensures consistent treatment of ground state correlations in the Fermi systems with pairing. The model is based on the generalized Green function formalism (GGFF) in which the normal and the anomalous Green functions are treated in a unified way in terms of the components of generalized Green functions in a space that is double the size of the usual single-particle space. Modification of the GGFF is considered in the case when the many-body nuclear Hamiltonian contains two-, three-, and other many-particle effective forces.
90 citations
TL;DR: In this paper, Coulomb screening and excitation spectra of electrons in a graphene layer with spin-orbit interaction (SOI) were studied in the random phase approximation, and an undamped plasmon mode emerges from the inter-band electron-hole excitation continuum edge and vanishes or merges with a Landau damped mode on the edge of the intra-band EH continuum.
Abstract: Coulomb screening and excitation spectra of electrons in a graphene layer with spin-orbit interaction (SOI) is studied in the random phase approximation. The SOI opens a gap between the valence and conduction bands of the semi-metal Dirac system and reshapes the bottom and top of the bands. As a result, we have observed a dramatic change in the long-wavelength dielectric function of the system. An undamped plasmon mode emerges from the inter-band electron-hole excitation continuum edge and vanishes or merges with a Landau damped mode on the edge of the intra-band electron-hole continuum. The characteristic collective excitation of the Dirac gas is recovered in a system with high carrier density or for a large wave vector.
86 citations
TL;DR: First results for atoms indicate that the random phase approximation overestimates correlation effects as much as the orbital-dependent functional obtained by a second order perturbation expansion on the basis of the Kohn-Sham Hamiltonian.
Abstract: The random phase approximation for the correlation energy functional of the density functional theory has recently attracted renewed interest. Formulated in terms of the Kohn-Sham orbitals and eigenvalues, it promises to resolve some of the fundamental limitations of the local density and generalized gradient approximations, as, for instance, their inability to account for dispersion forces. First results for atoms, however, indicate that the random phase approximation overestimates correlation effects as much as the orbital-dependent functional obtained by a second order perturbation expansion on the basis of the Kohn-Sham Hamiltonian. In this contribution, three simple extensions of the random phase approximation are examined; a its augmentation by a local density approximation for short-range correlation, b its combination with the second order exchange term, and c its combination with a partial resummation of the perturbation series including the second order exchange. It is found that the ground state and correlation energies as well as the ionization potentials resulting from the extensions a and c for closed subshell atoms are clearly superior to those obtained with the unmodified random phase approximation. Quite some effort is made to ensure highly converged data, so that the results may serve as benchmark data. The numerical techniques developed in this context, in particular, for the inherent frequency integration, should also be useful for applications of random phase approximation-type functionals to more complex systems. © 2007 American Institute of Physics. DOI: 10.1063/1.2795707
85 citations
TL;DR: In this paper, the same energy functional, i.e., the same set of coupling constants, generates the Dirac-Hartree single-particle spectrum, the static part of the residual p-h interaction, and the particle-phonon coupling vertices.
Abstract: Covariant density functional theory, which has so far been applied only within the framework of static and time-dependent mean-field theory, is extended to include particle-vibration coupling (PVC) in a consistent way. Starting from a conventional energy functional, we calculate the low-lying collective vibrations in the relativistic random phase approximation (RRPA) and construct an energy-dependent self-energy for the Dyson equation. The resulting Bethe-Salpeter equation in the particle-hole (p-h) channel is solved in the time blocking approximation (TBA). No additional parameters are used, and double counting is avoided by a proper subtraction method. The same energy functional, i.e., the same set of coupling constants, generates the Dirac-Hartree single-particle spectrum, the static part of the residual p-h interaction, and the particle-phonon coupling vertices. Therefore, a fully consistent description of nuclear excited states is developed. This method is applied for an investigation of damping phenomena in the spherical nuclei with closed shells $^{208}\mathrm{Pb}$ and $^{132}\mathrm{Sn}$. Since the phonon coupling terms enrich the RRPA spectrum with a multitude of p-h\ensuremath{\bigotimes}phonon components, a noticeable fragmentation of the giant resonances is found, which is in full agreement with experimental data and with results of the semiphenomenological nonrelativistic approach.
77 citations
TL;DR: In this article, the influence of antiferromagnetic order on the superconductivity in the non-centrosymmetric heavy fermion compound CePt 3 Si and related materials is discussed.
Abstract: The influence of antiferromagnetic order on the superconductivity in the non-centrosymmetric heavy fermion compound CePt 3 Si and related materials is discussed. Based on our RPA analysis for the extended Hubbard model two phases could be stabilized by a spin fluctuation induced pairing, with either dominantly p -wave or d -wave symmetry. The antiferromagnetic order plays an essential role for the low-energy physics, in particular, for the appearance of line nodes in the gap and the enhancement of spin susceptibility below T c . Various properties and possible phase diagrams under pressure are analyzed. The present experimental situation suggests that the p -wave phase is most likely realized in CePt 3 Si.
72 citations
TL;DR: It is shown that the direction of the dipole of the molecules determines the direction the polariton chooses and the precise position of the molecule has a significant effect on the transfer.
Abstract: Near-field interactions between plasmons and molecules are treated in a simple unified approach. The density matrix of a molecule is treated with linear-response random phase approximation and the plasmons are treated classically. The equations of motion for the combined system are linear, governed by a simple Liouvillian operator for the polariton (plasmon+molecule excitation) dynamics. The dynamics can be followed in time or directly in frequency space where a trace formula for the transmission is presented. A model system is studied, metal dots in a forklike arrangement, coupled to a two level system with a large transition-dipole moment. A Fano-type resonance [Phys. Rev. 103, 1202 (1956)] develops when the molecular response is narrower than the width of the absorption spectrum for the plasmons. We show that the direction of the dipole of the molecule determines the direction the polariton chooses. Further, the precise position of the molecule has a significant effect on the transfer.
66 citations
TL;DR: In this article, 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, Laradji and coworkers, 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, the electronic structure and magnetism of Mn-doped half-Heusler alloys were investigated by using the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method within the local density approximation (LDA).
Abstract: We have investigated the electronic structure and magnetism of Mn-doped half-Heusler alloys by using the Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA) method within the local density approximation (LDA). Half-Heusler compounds can be attractive for spintronic applications because the crystal structure and lattice constant of these compounds are similar to those of III–V and II–VI compounds, which are often used in present semiconductor technologies. The Curie temperatures of Mn-doped half-Heusler alloys are calculated by the mean field approximation, random phase approximation, and Monte Carlo simulation. Based on our calculation results, we discuss whether or not the half-Heusler-based dilute magnetic semiconductors are useful for realizing semiconductor spintronics.
TL;DR: In this paper, the absorption spectrum of semiconductors and insulators is compared with the Bethe-Salpeter equation of many-body perturbation theory and time-dependent density-functional theory using a recently developed kernel.
Abstract: We present calculations of the absorption spectrum of semiconductors and insulators comparing various approaches: (i) the two-particle Bethe-Salpeter equation of many-body perturbation theory; (ii) time-dependent density-functional theory using a recently developed kernel that was derived from the Bethe-Salpeter equation; and (iii) a mapping scheme that we propose in the present work and that allows one to derive different parameter-free approximations to (ii). We show that all methods reproduce the series of bound excitons in the gap of solid argon, as well as continuum excitons in semiconductors. This is even true for the simplest static approximation, which allows us to reformulate the equations in a way such that the scaling of the calculations with the number of atoms equals the one of the random phase approximation.
TL;DR: The low scaling prefactor and the satisfactory accuracy of the method makes TD‐DFTB especially suitable for molecular dynamics simulations of dozens of atoms as well as for the computation of luminescence spectra of systems containing hundreds of atoms.
Abstract: An analytical formulation for the geometrical derivatives of excitation energies within the time-dependent density-functional tight-binding (TD-DFTB) method is presented. The derivation is based on the auxiliary functional approach proposed in [Furche and Ahlrichs, J Chem Phys 2002, 117, 7433]. To validate the quality of the potential energy surfaces provided by the method, adiabatic excitation energies, excited state geometries, and harmonic vibrational frequencies were calculated for a test set of molecules in excited states of different symmetry and multiplicity. According to the results, the TD-DFTB scheme surpasses the performance of configuration interaction singles and the random phase approximation but has a lower quality than ab initio time-dependent density-functional theory. As a consequence of the special form of the approximations made in TD-DFTB, the scaling exponent of the method can be reduced to three, similar to the ground state. The low scaling prefactor and the satisfactory accuracy of the method makes TD-DFTB especially suitable for molecular dynamics simulations of dozens of atoms as well as for the computation of luminescence spectra of systems containing hundreds of atoms.
TL;DR: In this paper, the quasiparticle time blocking approximation (QTBA) was applied to describe E1 excitations in the even-even tin isotopes, and the main equations were written in the coordinate representation that allows to take into account single-particle continuum completely.
Abstract: The quasiparticle time blocking approximation (QTBA) is applied to describe E1 excitations in the even-even tin isotopes. Within the model pairing correlations, twoquasiparticle (2q), and 2q⊗phonon configurations are included. Thus the QTBA is an extension of the quasiparticle random phase approximation to include quasiparticlephonon coupling. Calculational formulas are presented in case of neutral excitations in the spherically symmetric system. The main equations are written in the coordinate representation that allows to take into account single-particle continuum completely. The E1 photoabsorption cross sections have been calculated in nuclei 116,120,124 Sn. It has been obtained that the 2q⊗phonon configurations provide noticeable fragmentation of the giant dipole resonance resulting in appearance of significant spreading width. The results are compared with available experimental data.
TL;DR: In this article, the relativistic random-phase approximation plus phonon-coupling model is applied in the analysis of E1 strength distributions in 208 Pb and 132 Sn, for which data on pygmy dipole resonances have recently been reported.
TL;DR: In this paper, the symmetry term of nuclear incompressibility was derived using the Thomas-Fermi approximation and the Coulomb term was also studied by using various different Skyrme Hamiltonians and RMF Lagrangians.
Abstract: The isospin dependence of incompressibility is investigated in Skyrme Hartree-Fock (SHF) and relativistic mean field (RMF) models. The correlations between the nuclear matter incompressibility and the isospin-dependent term of the finite nucleus incompressibility is elucidated using the Thomas-Fermi approximation. The Coulomb term is also studied by using various different Skyrme Hamiltonians and RMF Lagrangians. Microscopic $\mathrm{HF}+\mathrm{random}$ phase approximation (RPA) calculations are performed with Skyrme interactions for $^{208}\mathrm{Pb}$ and Sn isotopes to study the strength distributions of isoscalar giant monopole resonances. The symmetry term of nuclear incompressibility is extracted to be ${K}_{\ensuremath{\tau}}=\ensuremath{-}(500\ifmmode\pm\else\textpm\fi{}50)$ MeV from the recent experimental data of isoscalar giant monopole resonances (ISGMR) in Sn isotopes.
TL;DR: In this article, the spectral function of the closed-shell neon atom is computed by expanding the electron self-energy through a set of Faddeev equations, which describes the coupling of single-particle degrees of freedom with correlated two-electron, two-hole, and electron-hole pairs.
Abstract: The spectral function of the closed-shell neon atom is computed by expanding the electron self-energy through a set of Faddeev equations. This method describes the coupling of single-particle degrees of freedom with correlated two-electron, two-hole, and electron-hole pairs. The excitation spectra are obtained using the random-phase approximation (RPA), rather than the Tamm-Dancoff framework employed in the third-order algebraic diagrammatic construction method. The difference between these two approaches is studied, as well as the interplay between ladder and ring diagrams in the self-energy. Satisfactory results are obtained for the ionization energies as well as the energy of the ground state with the Faddeev RPA scheme, which is also appropriate for the high-density electron gas.
TL;DR: In this paper, the effects of short-range correlated disorder arising from chemical dopants or local lattice distortions on the ferromagnetism of 3D double exchange systems were studied.
Abstract: We study the effects of short-range-correlated disorder arising from chemical dopants or local lattice distortions on the ferromagnetism of 3d double exchange systems. For this, we integrate out the carriers and treat the resulting disordered spin Hamiltonian within a local random phase approximation, whose reliability is shown by direct comparison with Monte Carlo simulations. We find large-scale inhomogeneities in the charge, couplings, and spin densities. Compared with the homogeneous case, we obtain larger Curie temperatures TC and very small spin stiffnesses D. As a result, the large variations of D TC measured in manganites may be explained by correlated disorder. We also provide a microscopic model for Griffiths phases in double exchange systems.
TL;DR: This work compares the QMC binding energies with results obtained within the random phase approximation, finding significant quantitative differences and disagreement over the asymptotic behavior for bilayers at low densities.
Abstract: Quantum Monte Carlo (QMC) methods have been used to obtain accurate binding-energy data for pairs of parallel thin metallic wires and layers modeled by 1D and 2D homogeneous electron gases. We compare our QMC binding energies with results obtained within the random phase approximation, finding significant quantitative differences and disagreement over the asymptotic behavior for bilayers at low densities. We have calculated pair-correlation functions for metallic biwire and bilayer systems. Our QMC data could be used to investigate van der Waals energy functionals.
TL;DR: In this paper, the authors studied the properties of a dilute Bose condensed gas at zero temperature in the presence of a strong random potential with arbitrary correlation length and obtained a closed integral equation for the averaged density distribution which allows the determination of both the condensate and the superfluid density.
Abstract: We study the properties of a dilute Bose condensed gas at zero temperature in the presence of a strong random potential with arbitrary correlation length. Starting from the underlying Gross–Pitaevskii equation, we use the random phase approximation in order to get a closed integral equation for the averaged density distribution which allows the determination of both the condensate and the superfluid density. The obtained results generalise those of Huang and Meng (HM) to strong disorder. In particular, we find the critical value of the disorder strength, where the superfluid phase disappears by a first-order phase transition. We show how this critical value changes as a function of the correlation length.
TL;DR: In this paper, the results of first-principles computations for the lifetime of excited electrons in various metals are presented, in addition to crystalline systems also calculations of the electronic lifetimes in surface states of these materials are discussed.
TL;DR: In this paper, the authors theoretically study the CoO 2 -layer-thickness dependence of its magnetic and superconducting properties by analyzing a multiorbital Hubbard model using the random phase approximation.
Abstract: In order to understand the experimentally proposed phase diagrams of Na x CoO 2 · y H 2 O, we theoretically study the CoO 2 -layer-thickness dependence of its magnetic and superconducting (SC) properties by analyzing a multiorbital Hubbard model using the random phase approximation. When the Co valence s is +3.4, we show that the magnetic fluctuation exhibits a strong layer-thickness dependence, where it is enhanced at finite (zero) momentum in the thicker (thinner) layer system. A magnetic order phase appears sandwiched by two SC phases, consistent with the experiments. These two SC phases have different pairing states, where one is the singlet extended s -wave state and the other is the triplet p -wave state. On the other hand, only a triplet p -wave SC phase with a dome-shaped behavior of T c is predicted when s = +3.5, which is also consistent with the experiments. Controversial experimental results on the magnetic properties are also discussed.
TL;DR: In this paper, the properties of low lying and high lying electric dipole strength in the stable 40Ca, 44Ca and 48Ca isotopes have been calculated within the Extended Theory of Finite Fermi Systems (ETFFS).
TL;DR: In this paper, the authors studied the charge exchange spin-dipole (SD) excitations of Zr and Pb using Hartree-Fock(HF) + Random Phase approximation (RPA).
Abstract: Charge exchange spin-dipole (SD) excitations of $^{90}$Zr and $^{208}$Pb are studied by using a Skyrme
Hartree-Fock(HF) + Random Phase approximation (RPA). The calculated spin-dipole strength distributions are compared with experimental data obtained by $^{90}$Zr (p,n) $^{90}$Nb and $^{90}$Zr (n,p) $^{90}$ Nb reactions. The model-independent SD sum rule values of various Skyrme interactions are studied in comparison with the experimental values in order to determine the neutron skin thickness of $^{90}$Zr. The pressure of the neutron matter equation of state (EOS) and the nuclear matter symmetry energy are discussed in terms of the neutron skin thickness and peak energies of SD strength distributions.
TL;DR: In this article, a thermal and quantum-mechanical treatment of nuclear rotation using the formalism of the static path approximation plus the random-phase approximation is presented, which is free from infrared divergences.
Abstract: We present a thermal and quantum-mechanical treatment of nuclear rotation using the formalism of the static path approximation plus the random-phase approximation. Naive perturbation theory fails because of the presence of zero-frequency modes resulting from dynamical symmetry breaking. Such modes lead to infrared divergences. We show that composite zero-frequency excitations are properly treated within the collective coordinate method. The resulting perturbation theory is free from infrared divergences. Without the assumption of individual random spin vectors, we derive microscopically the spin distribution of the level density. The moment of inertia is thereby related to the spin-cutoff parameter in the usual way. Explicit calculations are performed for {sup 56}Fe; various thermal properties are discussed. In particular, we demonstrate that the increase of the moment of inertia with increasing temperature is correlated with the suppression of pairing correlations.
TL;DR: In this article, an extended version of the Hartree-Fock theory and the random phase approximation derived from the time-dependent density matrix theory (TDDM) are presented.
Abstract: Applications of an extended version of the Hartree-Fock theory and the random-phase approximation derived from the time-dependent density-matrix theory (TDDM) are presented. In this TDDM-based theory, the ground state is given as a stationary solution of the TDDM equations and the excited states are calculated using the small-amplitude limit of TDDM. The first application presented is an extended Lipkin model in which an interaction term describing a particle scattering is added to the original Hamiltonian so that the damping of a collective state is taken into account. It is found that the TDDM-based theory well reproduces the ground state and excited states of the extended Lipkin model. The quadrupole excitation of the oxygen isotopes $^{16,20,22}\mathrm{O}$ is also studied as realistic applications of the TDDM-based theory. It is found that large fragmentation of the giant quadrupole resonance in $^{16}\mathrm{O}$ is reproduced, and it is pointed out that the effects of ground-state correlations are quite important for fragmentation. It is also found that the quadrupole states in neutron-rich oxygen isotopes have small spreading widths.
TL;DR: It was shown that, among considered methods, the RPA provides most consistent and less time-consuming results for circular dichroism core excitation spectra.
Abstract: Soft x-ray natural circular dichroism of amino acids is studied by means of ab initio methods. Several approaches to evaluate the oscillator and rotary strengths of core-to-valence excitations are compared from the viewpoint of basis set dependence: ground-state Hartree-Fock (HF) orbital set employed in (i) random phase approximation (RPA), (ii) static exchange approach (STEX) (unrelaxed), (iii) core-ionized state HF orbital set applied in STEX (relaxed), and (iv) HF excited state orbital set for each core-to-valence excited state. Furthermore in (i) the PRA in the framework of the density functional method (DFT) is compared with the RPA where the ab initio HF orbital set is used. In (iv), the oscillator and rotary strengths evaluated by different orbital sets for the initial and final states, namely, nonorthogonal ground-state and core-excited HF orbitals, are compared with those evaluated by using the core-excited HF orbital set to describe the initial (ground) state. It was shown that, among considered methods, the RPA provides most consistent and less time-consuming results for circular dichroism core excitation spectra. Discussion of the low energy part of K edge circular dichroism spectra of five common amino acids obtained with the help of RPA is presented.
TL;DR: In this article, the quasiparticle and optical properties of BeH2 were computed by means of the all-electron GW approximation in conjunction with the projector augmented wave (PAW) method.
Abstract: The quasiparticle and optical properties of BeH2 are computed by means of the all-electron GW approximation in conjunction with the projector augmented wave (PAW) method. The GW approximation, through the calculation of the self-energy and the optical dielectric function in the random phase approximation, shows that BeH2 is a large band gap insulator. The results are discussed in view of future experiments.
TL;DR: In this article, the effect of exchange and correlation (XC) on the plasmon spectrum and the Coulomb drag between spatially separated low-density two-dimensional electron layers was investigated.
Abstract: We investigate the effect of exchange and correlation (XC) on the plasmon spectrum and the Coulomb drag between spatially separated low-density two-dimensional electron layers. We adopt a different approach, which employs dynamic XC kernels in the calculation of the bilayer plasmon spectra and of the plasmon-mediated drag, and static many-body local field factors in the calculation of the particle-hole contribution to the drag. The spectrum of bilayer plasmons and the drag resistivity are calculated in a broad range of temperatures taking into account both intra- and interlayer correlation effects. We observe that both plasmon modes are strongly affected by XC corrections. After the inclusion of the complex dynamic XC kernels, a decrease of the electron density induces shifts of the plasmon branches in opposite directions. This is in stark contrast with the tendency observed within random phase approximation that both optical and acoustical plasmons move away from the boundary of the particle-hole continuum with a decrease in the electron density. We find that the introduction of XC corrections results in a significant enhancement of the transresistivity and qualitative changes in its temperature dependence. In particular, the large high-temperature plasmon peak that is present in the random phase approximation is found to disappear when the XC corrections are included. Our numerical results at low temperatures are in good agreement with the results of recent experiments by Kellogg et al. [Solid State Commun. 123, 515 (2002)].