Showing papers on "Random phase approximation published in 2015"
TL;DR: In this article, a tight-binding model for black phosphorus (BP) with an arbitrary number of layers is presented, where the screened Coulomb interaction is calculated within the random phase approximation on the basis of density functional theory.
Abstract: We provide a tight-binding model parametrization for black phosphorus (BP) with an arbitrary number of layers. The model is derived from partially self-consistent $G{W}_{0}$ approach, where the screened Coulomb interaction ${W}_{0}$ is calculated within the random phase approximation on the basis of density functional theory. We thoroughly validate the model by performing a series of benchmark calculations, and determine the limits of its applicability. The application of the model to the calculations of electronic and optical properties of multilayer BP demonstrates good quantitative agreement with ab initio results in a wide energy range. We also show that the proposed model can be easily extended for the case of external fields, yielding the results consistent with those obtained from first principles. The model is expected to be suitable for a variety of realistic problems related to the electronic properties of multilayer BP including different kinds of disorder, external fields, and many-body effects.
196 citations
TL;DR: Electronic structure theories including all intermolecular interactions at equal footing, which requires the inclusion of non-local electron correlation, are used to describe structure and dynamics of bulk liquid water.
Abstract: Water is a ubiquitous liquid that displays a wide range of anomalous properties and has a delicate structure that challenges experiment and simulation alike. The various intermolecular interactions that play an important role, such as repulsion, polarization, hydrogen bonding, and van der Waals interactions, are often difficult to reproduce faithfully in atomistic models. Here, electronic structure theories including all these interactions at equal footing, which requires the inclusion of non-local electron correlation, are used to describe structure and dynamics of bulk liquid water. Isobaric-isothermal (NpT) ensemble simulations based on the Random Phase Approximation (RPA) yield excellent density (0.994 g/ml) and fair radial distribution functions, while various other density functional approximations produce scattered results (0.8-1.2 g/ml). Molecular dynamics simulation in the microcanonical (NVE) ensemble based on Moller-Plesset perturbation theory (MP2) yields dynamical properties in the condensed phase, namely, the infrared spectrum and diffusion constant. At the MP2 and RPA levels of theory, ice is correctly predicted to float on water, resolving one of the anomalies as resulting from a delicate balance between van der Waals and hydrogen bonding interactions. For several properties, obtaining quantitative agreement with experiment requires correction for nuclear quantum effects (NQEs), highlighting their importance, for structure, dynamics, and electronic properties. A computed NQE shift of 0.6 eV for the band gap and absorption spectrum illustrates the latter. Giving access to both structure and dynamics of condensed phase systems, non-local electron correlation will increasingly be used to study systems where weak interactions are of paramount importance.
95 citations
TL;DR: In this paper, Michta et al. showed that the SE potential is qualitatively different from the full potential, whereas the SM potential and AM potential are significantly more accurate at any temperature and the AM potential at zero temperature.
Abstract: The effective potential Φ of a classical ion in a weakly correlated quantum plasma in thermodynamic equilibrium at finite temperature is well described by the random phase approximation screened Coulomb potential. Additionally, collision effects can be included via a relaxation time ansatz (Mermin dielectric function). These potentials are used to study the quality of various statically screened potentials that were recently proposed by Shukla and Eliasson (SE) [Phys. Rev. Lett. 108, 165007 (2012)], Akbari-Moghanjoughi (AM) [Phys. Plasmas 22, 022103 (2015)], and Stanton and Murillo (SM) [Phys. Rev. E 91, 033104 (2015)] starting from quantum hydrodynamic (QHD) theory. Our analysis reveals that the SE potential is qualitatively different from the full potential, whereas the SM potential (at any temperature) and the AM potential (at zero temperature) are significantly more accurate. This confirms the correctness of the recently derived [Michta et al., Contrib. Plasma Phys. 55, 437 (2015)] pre-factor 1/9 in front of the Bohm term of QHD for fermions.
95 citations
TL;DR: In this article, an extension of the Majorana neutrino mass mechanism of the neutrinoless double-beta decay (0νββ) with the inclusion of right-handed leptonic and hadronic currents is revisited.
Abstract: The extension of the Majorana neutrino mass mechanism of the neutrinoless double-beta decay (0νββ) with the inclusion of right-handed leptonic and hadronic currents is revisited. While only the exchange of light neutrinos is assumed, the s_(1/2) and p_(1/2) states of emitted electrons as well as recoil corrections to the nucleon currents are taken into account. Within the standard approximations the decay rate is factorized into a sum of products of kinematical phase-space factors, nuclear matrix elements, and the fundamental parameters that characterize the lepton number violation. Unlike in the previous treatments, the induced pseudoscalar term of hadron current is included, resulting in additional nuclear matrix elements. An improved numerical computation of the phase-space factors is presented, based on the exact Dirac wave functions of the s_(1/2) and p_(1/2) electrons with finite nuclear size and electron screening taken into account. The dependence of values of these phase-space factors on the different approximation schemes used in evaluation of electron wave functions is discussed. The upper limits for effective neutrino mass and the parameters ⟨λ⟩ and ⟨η⟩ characterizing the right-handed current mechanism are deduced from data on the 0νββ decay of ^(76)Ge and ^(136)Xe using nuclear matrix elements calculated within the nuclear shell model and quasiparticle random phase approximation. The differential decay rates, i.e., the angular correlations and the single electron energy distributions for various combinations of the total lepton number violating parameters that can help to disentangle the possible mechanism, are described and discussed.
69 citations
TL;DR: In this article, the authors considered the plasmon mode arising in three-dimensional Dirac liquids, i.e., systems with linear chiral relativistic single-particle dispersion, within the random phase approximation.
Abstract: We consider theoretically as a function of temperature the plasmon mode arising in three-dimensional Dirac liquids, i.e., systems with linear chiral relativistic single-particle dispersion, within the random phase approximation. We find that whereas no plasmon mode exists in the intrinsic (undoped) system at zero temperature, there is a well-defined finite-temperature plasmon with superlinear temperature dependence, rendering the plasmon dispersion widely tunable with temperature. The plasmon dispersion contains a logarithmic correction due to the ultraviolet-logarithmic renormalization of the electron charge, manifesting a fundamental many-body interaction effect as in quantum electrodynamics. The plasmon dispersion of the extrinsic (doped) system displays a minimum at finite temperature before it crosses over to the superlinear intrinsic behavior at higher temperature, implying that the high-temperature plasmon is a universal feature of Dirac liquids irrespective of doping. This striking characteristic temperature dependence of intrinsic Dirac plasmons along with the logarithmic renormalization is a unique manifestation of the three-dimensional relativistic Dirac nature of quasiparticle excitations and serves as an experimentally observable signature of three-dimensional Dirac materials.
68 citations
TL;DR: In this paper, the electronic and linear optical properties of hexagonal boron nitride (h-BN) nanosheet using the full potential linearized augmented plane wave method in the framework of the density functional theory were investigated.
66 citations
TL;DR: A stochastic approach to time-dependent density functional theory is developed for computing the absorption cross section and the random phase approximation (RPA) correlation energy and it is found that the overall scaling of the algorithm is sublinear with computational time and memory.
Abstract: A stochastic approach to time-dependent density functional theory is developed for computing the absorption cross section and the random phase approximation (RPA) correlation energy. The core idea of the approach involves time-propagation of a small set of stochastic orbitals which are first projected on the occupied space and then propagated in time according to the time-dependent Kohn-Sham equations. The evolving electron density is exactly represented when the number of random orbitals is infinite, but even a small number (≈16) of such orbitals is enough to obtain meaningful results for absorption spectrum and the RPA correlation energy per electron. We implement the approach for silicon nanocrystals using real-space grids and find that the overall scaling of the algorithm is sublinear with computational time and memory.
50 citations
TL;DR: Nuclear β decay in magic nuclei is investigated, taking into account the coupling between particles and collective vibrations, on top of self-consistent random phase approximation calculations based on Skyrme density functionals, leading to very good agreement between theoretical and experimental lifetimes.
Abstract: Nuclear $\ensuremath{\beta}$ decay in magic nuclei is investigated, taking into account the coupling between particles and collective vibrations, on top of self-consistent random phase approximation calculations based on Skyrme density functionals. The low-lying Gamow-Teller strength is shifted downwards and at times becomes fragmented; as a consequence, the $\ensuremath{\beta}$-decay half-lives are reduced due to the increase of the phase space available for the decay. In some cases, this leads to a very good agreement between theoretical and experimental lifetimes: this happens, in particular, in the case of the Skyrme force SkM* that can also reproduce the line shape of the high-energy Gamow-Teller resonance as was previously shown.
48 citations
TL;DR: In this article, a theory for electron-electron interaction-induced many-body effects in three-dimensional Weyl or Dirac semimetals, including interaction corrections to the polarizability, electron self-energy, and vertex function, up to second order in the effective fine-structure constant of the Dirac material, was developed.
Abstract: We develop a theory for electron-electron interaction-induced many-body effects in three-dimensional Weyl or Dirac semimetals, including interaction corrections to the polarizability, electron self-energy, and vertex function, up to second order in the effective fine-structure constant of the Dirac material. These results are used to derive the higher-order ultraviolet renormalization of the Fermi velocity, effective coupling, and quasiparticle residue, revealing that the corrections to the renormalization group flows of both the velocity and coupling counteract the leading-order tendencies of velocity enhancement and coupling suppression at low energies. This in turn leads to the emergence of a critical coupling above which the interaction strength grows with decreasing energy scale. In addition, we identify a range of coupling strengths below the critical point in which the Fermi velocity varies nonmonotonically as the low-energy, noninteracting fixed point is approached. Furthermore, we find that while the higher-order correction to the flow of the coupling is generally small compared to the leading order, the corresponding correction to the velocity flow carries an additional factor of the Dirac cone flavor number (the multiplicity of electron species, e.g. ground-state valley degeneracy arising from the band structure) relative to the leading-order result. Thus, for materials with a larger multiplicity, the regime of velocity nonmonotonicity is reached for modest values of the coupling strength. This is in stark contrast to an approach based on a $\text{large}\ensuremath{-}N$ expansion or the random phase approximation (RPA), where higher-order corrections are strongly suppressed for larger values of the Dirac cone multiplicity. This suggests that perturbation theory in the coupling constant (i.e., the loop expansion) and the $\text{RPA}/\text{large}\ensuremath{-}N$ expansion are complementary in the sense that they are applicable in different parameter regimes of the theory. We show how our results for the ultraviolet renormalization of quasiparticle properties can be tested experimentally through measurements of quantities such as the optical conductivity or dielectric function (with carrier density or temperature acting as the scale being varied to induce the running coupling). Although experiments typically access the finite-density regime, we show that our zero-density results still capture clear many-body signatures that should be visible at higher temperatures even in real systems with disorder and finite doping.
48 citations
TL;DR: In this paper, the collective plasmon excitations and screening of pure and disordered single and bilayer black phosphorus (BP) beyond the low energy continuum approximation were studied.
Abstract: We study collective plasmon excitations and screening of pure and disordered single- and bilayer black phosphorus (BP) beyond the low energy continuum approximation. The dynamical polarizability of phosphorene is computed using a tight-binding model that properly accounts for the band structure in a wide energy range. Electron-electron interaction is considered within the random phase approximation. Damping of the plasmon modes due to different kinds of disorder, such as resonant scatterers and long-range disorder potentials, is analyzed. We further show that an electric field applied perpendicular to bilayer phosphorene can be used to tune the dispersion of the plasmon modes. For sufficiently large electric field, the bilayer BP enters in a topological phase with a characteristic plasmon spectrum, which is gaped in the armchair direction.
43 citations
TL;DR: This work confirms range-separated RPAx-SO2 as a promising method for general chemical applications and shows that range separation greatly improves the accuracy of all RPA variants for these properties.
Abstract: We consider several spin-unrestricted random-phase approximation (RPA) variants for calculating correlation energies, with and without range separation, and test them on datasets of atomization energies and reaction barrier heights. We show that range separation greatly improves the accuracy of all RPA variants for these properties. Moreover, we show that a RPA variant with exchange, hereafter referred to as RPAx-SO2, first proposed by Szabo and Ostlund [J. Chem. Phys. 67, 4351 (1977)] in a spin-restricted closed-shell formalism, and extended here to a spin-unrestricted formalism, provides on average the most accurate range-separated RPA variant for atomization energies and reaction barrier heights. Since this range-separated RPAx-SO2 method had already been shown to be among the most accurate range-separated RPA variants for weak intermolecular interactions [J. Toulouse et al., J. Chem. Phys. 135, 084119 (2011)], this works confirms range-separated RPAx-SO2 as a promising method for general chemical applications.
TL;DR: In this article, the authors studied the properties of the interacting Dirac liquid, a three-dimensional many-body system which was recently experimentally realized and in which the electrons have a chiral linear relativistic dispersion and a mutual Coulomb interaction.
Abstract: We study theoretically the properties of the interacting Dirac liquid, a novel three-dimensional many-body system which was recently experimentally realized and in which the electrons have a chiral linear relativistic dispersion and a mutual Coulomb interaction. We find that the ``intrinsic'' Dirac liquid, where the Fermi energy lies exactly at the nodes of the band dispersion, displays unusual Fermi liquid properties similar to graphene, whereas the ``extrinsic'' system with finite detuning or doping behaves as a standard Landau Fermi liquid. We present analytical and numerical results for the self-energy and spectral function based on both Hartree-Fock and the random phase approximation (RPA) theories and compute the quasiparticle lifetime, residue, and renormalized Fermi velocity of the extrinsic Dirac liquid. A full numerical calculation of the extrinsic RPA spectral function indicates that the Fermi liquid description breaks down for large-energy excitations. Furthermore, we find an additional plasmaron quasiparticle sideband in the spectral function which is discontinuous around the Fermi energy. Our predictions should be observable in ARPES and STM measurements.
TL;DR: In this paper, the authors make use of a subtraction procedure, introduced to overcome double counting problems in beyond-mean-field theories, in the second random phase approximation (SRPA) for the first time.
Abstract: We make use of a subtraction procedure, introduced to overcome double--counting problems in beyond--mean--field theories, in the second random--phase--approximation (SRPA) for the first time. This procedure guarantees the stability of SRPA (so that all excitation energies are real). We show that the method fits perfectly into nuclear density--functional theory. We illustrate applications to the monopole and quadrupole response and to low--lying $0^+$ and $2^+$ states in the nucleus $^{16}$O. We show that the subtraction procedure leads to: (i) results that are weakly cutoff dependent; (ii) a considerable reduction of the SRPA downwards shift with respect to the random--phase approximation (RPA) spectra (systematically found in all previous applications). This implementation of the SRPA model will allow a reliable analysis of the effects of 2 particle--2 hole configurations ($2p2h$) on the excitation spectra of medium--mass and heavy nuclei.
TL;DR: This paper presents a formalism for derivative couplings between time-dependent density functional theory (TD-DFT) excited states within the randomphase approximation (RPA) using analytic gradient theory, based on a pseudo-wavefunction approach in a companion paper.
Abstract: In this paper, we present a formalism for derivative couplings between time-dependent density functional theory (TD-DFT) excited states within the random- phase approximation (RPA) using analytic gradient theory. Our formalism is based on a pseudo-wavefunction approach in a companion paper (DOI 10.1021/jp505767b), and can be checked against finite-difference overlaps. Our approach recovers the correct properties of derivative couplings around a conical intersection (CI), which is a crucial prerequisite for any derivative coupling expression. As an example, we study the test case of protonated formaldimine (CH2NH2 + ).
TL;DR: In this article, the authors explore the relevance of singles contributions for prototypical solid state systems and discuss the physical relevance and importance of singles alongside illustrative examples of simple weakly bonded systems, including rare gas solids, ice, adsorption of water on NaCl, and solid benzene.
Abstract: The random phase approximation to the correlation energy often yields highly accurate results for condensed matter systems. However, ways how to improve its accuracy are being sought and here we explore the relevance of singles contributions for prototypical solid state systems. We set out with a derivation of the random phase approximation using the adiabatic connection and fluctuation dissipation theorem, but contrary to the most commonly used derivation, the density is allowed to vary along the coupling constant integral. This yields results closely paralleling standard perturbation theory. We re-derive the standard singles of Gorling-Levy perturbation theory [A. Gorling and M. Levy, Phys. Rev. A 50, 196 (1994)], highlight the analogy of our expression to the renormalized singles introduced by Ren and coworkers [Phys. Rev. Lett. 106, 153003 (2011)], and introduce a new approximation for the singles using the density matrix in the random phase approximation. We discuss the physical relevance and importance of singles alongside illustrative examples of simple weakly bonded systems, including rare gas solids (Ne, Ar, Xe), ice, adsorption of water on NaCl, and solid benzene. The effect of singles on covalently and metallically bonded systems is also discussed.
TL;DR: In this article, the residual interaction of infinite nuclear matter with arbitrary isospin asymmetry is derived from a general nuclear Skyrme energy density functional, including the usual central, spin-orbit and tensor terms, as well as new density-dependent terms or three-body terms.
TL;DR: In this article, the doping evolution of spin and charge excitations in the single-band Hubbard model using determinant quantum Monte Carlo (DQMC) was examined, and significant residual correlations in the two-particle excitations persist up to 40% hole and 15% electron doping.
Abstract: To shed light on how electronic correlations vary across the phase diagram of the cuprate superconductors, we examine the doping evolution of spin and charge excitations in the single-band Hubbard model using determinant quantum Monte Carlo (DQMC). In the single-particle response, we observe that the effects of correlations weaken rapidly with doping, such that one may expect the random phase approximation (RPA) to provide an adequate description of the two-particle response. In contrast, when compared to RPA, we find that significant residual correlations in the two-particle excitations persist up to 40% hole and 15% electron doping (the range of dopings achieved in the cuprates). These fundamental differences between the doping evolution of single- and multiparticle renormalizations show that conclusions drawn from single-particle processes cannot necessarily be applied to multiparticle excitations. Eventually, the system smoothly transitions via a momentum-dependent crossover into a weakly correlated metallic state where the spin and charge excitation spectra exhibit similar behavior and where RPA provides an adequate description.
TL;DR: In this article, the authors presented self-consistent calculations of isoscalar giant monopole and quadrupole as well as isovector giant dipole resonances in heavy and light nuclei.
TL;DR: In this article, a deformed proton-neutron quasiparticle random-phase approximation of the underlying mean field is described self-consistently from deformed Skyrme-Hartree-Fock calculations with pairing correlations.
Abstract: $\ensuremath{\beta}$-decay properties of even- and odd-$A$ neutron-rich Ge, Se, Kr, Sr, Ru, and Pd isotopes involved in the astrophysical rapid neutron capture process are studied within a deformed proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme-Hartree-Fock calculations with pairing correlations. Residual interactions in the particle-hole and particle-particle channels are also included in the formalism. The isotopic evolution of the various nuclear equilibrium shapes and the corresponding charge radii are investigated in all the isotopic chains. The energy distributions of the Gamow-Teller strength as well as the $\ensuremath{\beta}$-decay half-lives are discussed and compared with the available experimental information. It is shown that nuclear deformation plays a significant role in the description of the decay properties in this mass region. Reliable predictions of the strength distributions are essential to evaluate decay rates in astrophysical scenarios.
TL;DR: In this paper, a microscopic nuclear reaction model is applied to neutron elastic and direct inelastic scatterings, and pre-equilibrium reaction, and a JLM folding model is used with nuclear structure information calculated within the quasi-particle random phase approximation implemented with the Gogny D1S interaction.
Abstract: A microscopic nuclear reaction model is applied to neutron elastic and direct inelastic scatterings, and pre-equilibrium reaction. The JLM folding model is used with nuclear structure information calculated within the quasi-particle random phase approximation implemented with the Gogny D1S interaction. The folding model for direct inelastic scattering is extended to include rearrangement corrections stemming from both isoscalar and isovector density variations occurring during a transition. The quality of the predicted (n,n), (n,
$n^{\prime}$
), (n,xn) and (
$n,n^{\prime}\gamma$
cross sections, as well as the generality of the present microscopic approach, shows that it is a powerful tool that can help improving nuclear reactions data quality. Short- and long-term perspectives are drawn to extend the present approach to more systems, to include missing reactions mechanisms, and to consistently treat both structure and reaction problems.
TL;DR: In this paper, the dispersions of the charge and spin modes and their coupling to each other within a generalized Random Phase Approximation for arbitrarily strong spin-orbit coupling (SOC) was studied both in 2D and 3D systems.
Abstract: In addition to charge plasmons, a 2D electron system with Rashba-type spin-orbit coupling (SOC) also supports three collective modes in the spin sector: the chiral-spin modes. We study the dispersions of the charge and spin modes and their coupling to each other within a generalized Random Phase Approximation for arbitrarily strong SOC, and both in 2D and 3D systems. In both 2D and 3D, we find that the charge plasmons are coupled to only one of the three chiral-spin modes. This coupling is shown to affect the dispersions of the modes at finite but not at zero wavenumbers. In 3D, the chiral-spin modes are strongly damped by particle-hole excitations and disappear for weak electron-electron interaction. Landau damping of the chiral-spin modes in 3D is directly related to the fact that, in contrast to 2D, there is no gap for particle-hole excitations between spin-split subbands. The gapless continuum is also responsible for Landau damping of the charge plasmon in 3D - a qualitatively new feature of the SOC system. We also discuss the optical conductivity of clean 2D and 3D systems and show that SOC introduces spectral weight at finite frequency in a such way that the sum rule is satisfied. The in-plane tranverse chiral-spin mode shows up as dispersing peak in the optical conductivity at finite number which can can be measured in the presence of diffraction grating. We also discuss possible experimental manifestations of chiral-spin modes in semiconductor quantum wells such InGaAs/AlGaAs and 3D giant Rashba materials of the BiTeI family.
TL;DR: The analytic excited state energy gradient of the particle-particle random phase approximation (pp-RPA) is presented, developed from an approach similar to that of time-dependent density-functional theory (TDDFT).
Abstract: The energy gradient for electronic excited states is of immense interest not only for spectroscopy but also for the theoretical study of photochemical reactions. We present the analytic excited state energy gradient of the particle-particle random phase approximation (pp-RPA). The analytic gradient formula is developed from an approach similar to that of time-dependent density-functional theory (TDDFT). The formula is verified for both the Hartree–Fock and (Generalized) Kohn–Sham reference states via comparison with finite difference results. The excited state potential energy surfaces and optimized geometries of some small molecules are investigated, yielding results of similar or better quality compared to adiabatic TDDFT. The singlet-to-triplet instability in TDDFT resulting in underestimated energies of the lowest triplet states is eliminated by pp-RPA. Charge transfer excitations and double excitations, which are challenging for most adiabatic TDDFT methods, can be reasonably well captured by pp-RPA. Within this framework, ground state potential energy surfaces of stretched single bonds can also be described well.
TL;DR: In this paper, the long-wavelength static screening properties of both neutral and doped graphene in the framework of density-functional theory were calculated using a plane-wave approach with periodic images in the third dimension and truncate the Coulomb interactions to eliminate spurious interlayer screening.
Abstract: We calculate the long-wavelength static screening properties of both neutral and doped graphene in the framework of density-functional theory We use a plane-wave approach with periodic images in the third dimension and truncate the Coulomb interactions to eliminate spurious interlayer screening We carefully address the issue of extracting two-dimensional dielectric properties from simulated three-dimensional potentials We compare this method with analytical expressions derived for two-dimensional massless Dirac fermions in the random phase approximation We evaluate the contributions of the deviation from conical bands, exchange correlation, and local fields For momenta smaller than twice the Fermi wave vector, the static screening of graphene within the density-functional perturbative approach agrees with the results for conical bands within the random phase approximation and neglecting local fields For larger momenta, we find that the analytical model underestimates the static dielectric function by $\ensuremath{\approx}10%$, mainly due to the conical band approximation
TL;DR: In this article, the reliability of the constrained random phase approximation (cRPA) method for the calculation of low-energy effective Hamiltonians by considering multi-orbital lattice models with one strongly correlated "target" band and two weakly correlated "screening" bands is investigated.
Abstract: We study the reliability of the constrained random phase approximation (cRPA) method for the calculation of low-energy effective Hamiltonians by considering multi-orbital lattice models with one strongly correlated "target" band and two weakly correlated "screening" bands. The full multi-orbital system and the effective model are solved within dynamical mean field theory (DMFT) in a consistent way. By comparing the quasi-particle weights for the correlated bands, we examine how accurately the effective model describes the low-energy properties of the multi-band system. We show that the violation of the Pauli principle in the cRPA method leads to overscreening effects when the inter-orbital interaction is small. This problem can be overcome by using a variant of the cRPA method which restores the Pauli principle.
TL;DR: An inclusion of the Lorentz friction to the damping of plasmons in metallic nanosphere is performed within the random phase approximation quasiclassical approach and the theory with accurately included LorentZ friction is demonstrated.
Abstract: An inclusion of the Lorentz friction to the damping of plasmons in metallic nanosphere is performed within the random phase approximation quasiclassical approach. The explanation of the experimentally observed anomalous red shift of plasmon resonance frequency with increase of the metallic particle radius for a large size limit is given and the perfect coincidence of the measured plasmon resonance red shift for Au nanospheres with radii 10 – 75 nm and the theory with accurately included Lorentz friction is demonstrated.
TL;DR: In this article, a covariant multiphonon response theory is developed and adopted for nuclear structure calculations in medium-mass and heavy nuclei, which is formulated in both general and coupled forms in the spherical basis.
Abstract: Background: Nuclear excited states within a wide range of excitation energies are formally described by linear response theory. Besides its conventional formulation within the quasiparticle random phase approximation representing excited states as two correlated quasiparticles, there exist extensions for four-quasiparticle configurations. Such extended approaches are quite successful in the description of gross properties of nuclear spectra; however, accounting for many of their fine features requires further extension of the configuration space.Purpose: This work aims at the development of an approach which is capable of such an extension as well as of reproducing and predicting fine spectral properties, which are of special interest at low energies.Method: The method is based on covariant density functional theory and the time-blocking approximation, which is extended for couplings between quasiparticles and multiphonon excitations.Results: A covariant multiphonon response theory is developed and adopted for nuclear structure calculations in medium-mass and heavy nuclei. The equations are formulated in both general and coupled forms in the spherical basis.Conclusions: The developed covariant multiphonon response theory represents a new generation of approaches to nuclear response, which aims at a unified description of both high-frequency collective states and low-energy spectroscopy in medium-mass and heavy nuclei.
TL;DR: In this article, the authors examined fractional charge and spin errors in self-consistent Green's function theory within a second-order approximation (GF2) and showed that GF2 has both less fractional charges and fractional spin errors than typical hybrid density functionals as well as random phase approximation with exchange.
Abstract: We examine fractional charge and spin errors in self-consistent Green's function theory within a second-order approximation (GF2). For GF2 it is known that the summation of diagrams resulting from the self-consistent solution of the Dyson equation removes the divergences pathological to second-order Moller-Plesset theory (MP2) for strong correlations. In the language often used in density functional theory contexts, this means GF2 has a greatly reduced fractional spin error relative to MP2. The natural question then is what effect, if any, does the Dyson summation have on the fractional charge error in GF2? To this end we generalize our previous implementation of GF2 to open-shell systems and analyze its fractional spin and charge errors. We find that like MP2, GF2 possesses only a very small fractional charge error, and consequently little many electron self-interaction error. This shows that GF2 improves on the critical failings of MP2, but without altering the positive features that make it desirable. Furthermore, we find that GF2 has both less fractional charge and fractional spin errors than typical hybrid density functionals as well as random phase approximation with exchange.
TL;DR: In this article, the authors exploit this feature to add the missing correlation to these methods via meta-GGA density functionals (TPSS and SCAN) and improve upon these CCD0+DFT blends by invoking range separation, which corrects the description of long-range van der Waals forces.
Abstract: Contrary to standard coupled cluster doubles (CCD) and Brueckner doubles (BD), singlet-paired analogues of CCD and BD (denoted here as CCD0 and BD0) do not break down when static correlation is present, but neglect substantial amounts of dynamic correlation. In fact, CCD0 and BD0 do not account for any contributions from multielectron excitations involving only same-spin electrons at all. We exploit this feature to add---without introducing double counting, self-interaction, or increase in cost---the missing correlation to these methods via meta-GGA density functionals (TPSS and SCAN). Furthermore, we improve upon these CCD0+DFT blends by invoking range separation: the short- and long-range correlations absent in CCD0/BD0 are evaluated with DFT and the direct random phase approximation (dRPA), respectively. This corrects the description of long-range van der Waals forces. Comprehensive benchmarking shows that the combinations presented here are very accurate for weakly correlated systems, while also providing a reasonable description of strongly correlated problems without resorting to symmetry breaking.
TL;DR: In this article, the energy dependence of first scattering phases with multiatomic objects was studied and it appeared that the presence of an inner atom, either Ne or Ar, qualitatively affects the scattering phases, in spite of the fact that the fullerene consists of 60 carbon atoms.
Abstract: We have studied the energy dependence of several first scattering phases with multiatomic object. As concrete examples representing the general trends endohedrals Ne@C60 and Ar@C60 are considered. It appeared that the presence of an inner atom, either Ne or Ar, qualitatively affects the scattering phases, in spite of the fact that the fullerene consists of 60 carbon atoms, while the atom staffed inside is only one. Calculations are performed in the one-electron Hartree-Fock (HF) and random phase approximation with exchange (RPAE) for the inner atom while the fullerenes shell is substituted by static potential without and with the polarization potential. It appeared that the total endohedral scattering phase is simply a sum of atomic, Ne or Ar, and fullerenes C60 phases, contrary to the intuitive assumption that the total phases on C60 and Ne@C60 or Ar@C60 has to be the same.
TL;DR: In this paper, the authors carried out first-principles calculations of the quasi-particle band structure and optical absorption spectra of H-passivated armchair MoS2 nanoribbons (AMoS2NRs) by employing the approach combining the Green's function perturbation theory and the Bethe-Salpeter equation (BSE), i.e., GW+BSE.
Abstract: We carry out first-principles calculations of the quasi-particle band structure and optical absorption spectra of H-passivated armchair MoS2 nanoribbons (AMoS2NRs) by employing the approach combining the Green’s function perturbation theory (GW) and the Bethe-Salpeter equation (BSE), i.e., GW+BSE. Optical absorption spectra of AMoS2NRs show the exciton multibands (their binding energies are close to or less than 1 eV) which are much stronger than a single layer of MoS2. However, they are absent in the spectra by the approach of GW and the random phase approximation (RPA), i.e., GW+RPA. This signifies that the excitonic correlation effects are strongly enhanced in the reduced dimensional structure of MoS2. We also calculate the exciton wave functions for the few lowest energy excitons, which are found to have non-Frenkel character.