Real-time cumulant approach for charge-transfer satellites in x-ray photoemission spectra

Kas, J. J.; Vila, Fernando D.; Rehr, J. J.; Chambers, Scott A.

doi:10.1103/physrevb.91.121112

Cited by 46 publications

(45 citation statements)

References 45 publications

(107 reference statements)

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“…The cumulant approach has been successful at zero T in elucidating correlation effects beyond the GW approximation of MBPT in a variety of contexts [27][28][29][30][31][32]. For example, in contrast to GW , the approach explains the multiple-plasmon satellites observed in x-ray photoemission spectra (XPS) [27,[33][34][35][36].…”

mentioning

confidence: 99%

Finite Temperature Green’s Function Approach for Excited State and Thermodynamic Properties of Cool to Warm Dense Matter

Kas

Rehr

2017

Phys. Rev. Lett.

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We present a finite-temperature extension of the retarded cumulant Green's function for calculations of exited-state and thermodynamic properties of electronic systems. The method incorporates a cumulant to leading order in the screened Coulomb interaction W and improves excited state properties compared to the GW approximation of many-body perturbation theory. Results for the homogeneous electron gas are presented for a wide range of densities and temperatures, from cool to warm dense matter regime, which reveal several hitherto unexpected properties. For example, correlation effects remain strong at high T while the exchange-correlation energy becomes small. In addition, the spectral function broadens and damping increases with temperature, blurring the usual quasi-particle picture. Similarly Compton scattering exhibits substantial many-body corrections that persist at normal densities and intermediate T . Results for exchange-correlation energies and potentials are in good agreement with existing theories and finite-temperature DFT functionals. Finite temperature (FT) effects in electronic systems are both of fundamental interest and practical importance. These effects vary markedly depending on whether the temperature T is larger or smaller than the Fermi temperature T F (typically a few eV). At "cool" temperatures, where T is much smaller than T F , electrons are nearly degenerate, and Fermi factors and excitations such as phonons dominate the thermal behavior [1][2][3]. In contrast thermal occupations become nearly semi-classical and electronic excitations such as plasmons become important in the warm-dense-matter (WDM) regime, where T is of order T F or larger, and condensed matter is partially ionized. Recently there has been considerable interest in both experimental and theoretical investigations of WDM for applications ranging from laser-shocked systems and inertial confinement fusion to astrophysics [4,5]. Many of these studies focus on equilibrium thermodynamic properties, e.g., using the FT generalization of density functional theory (DFT) [6][7][8]. Although in principle, FT DFT is exact [9][10][11], practical applications require exchange-correlation functionals which must be approximated, e.g., by constrained fits [12] to theoretical electron gas calculations [8,[13][14][15][16][17]. However, these approaches have various limitations. First, many materials properties such as optical and x-ray spectra depend on quasi-particle or excited-state effects. For example, band-gaps depend on quasi-particle energies, and calculations of x-ray spectra [18] and Compton scattering require correlation corrections [19]. Although methods like quantum Monte-Carlo and the random phase approximation (RPA) can provide accurate correlation energies, they are not directly applicable to such excited state properties. Secondly, currently available exchangecorrelation functionals can exhibit unphysical behavior outside the range of validity of theoretical data [20]. On the other hand Green's function (GF) methods within...

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confidence: 99%

Finite Temperature Green’s Function Approach for Excited State and Thermodynamic Properties of Cool to Warm Dense Matter

Kas

Rehr

2017

Phys. Rev. Lett.

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“…This is advantageous computationally as the physics of the intrinsic and extrinsic losses can differ significantly. Here we treat the intrinsic losses with the cumulant C c (t) for the core-hole Green's function using a real-space, realtime method of Kas et al (KVRC), 23 as described below. This local approach was found to account well for charge-transfer satellites in the XPS of transition metal oxides.…”

Section: Theorymentioning

confidence: 99%

“…The localized nature of a deep core-hole in x-ray spectra has led us to consider a real-space, real-time approach for the intrinsic cumulant C c (t) introduced by KVRC, 23 which is not limited to small clusters. Our treatment is based on a time-dependent density functional theory formalism (RT-TDDFT) inspired by that of Bertsch and Yabana 24 for optical response.…”

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confidence: 99%

Particle-hole cumulant approach for inelastic losses in x-ray spectra

2016

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Inelastic losses in core level x-ray spectra arise from many-body excitations, leading to broadening and damping as well as satellite peaks in x-ray photoemission (XPS) and x-ray absorption (XAS) spectra. Here we present a practical approach for calculating these losses based on a cumulant representation of the particle-hole Green's function, a quasi-boson approximation, and a partition of the cumulant into extrinsic, intrinsic and interference terms. The intrinsic losses are calculated using real-time, time-dependent density functional theory while the extrinsic losses are obtained from the GW approximation of the photo-electron self-energy and the interference terms are approximated. These effects are included in the spectra using a convolution with an energy dependent particle-hole spectral function. The approach elucidates the nature of the spectral functions in XPS and XAS and explains the significant cancellation between extrinsic and intrinsic losses. Edge-singularity effects in metals are also accounted for. Illustrative results are presented for the XPS and XAS for both weakly and more correlated systems.

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“…Still, while the high-frequency behavior of W calculated from the random phase approximation is often a good approximation to the true one, exhibiting in particular satellite structures at the plasma energy of the system, its use in the first order formula Σ = GW leads to artefacts: when used to recalculate the Green's function (and from it, the spectral function) the use of the GW self-energy truncates the series of plasmon replicae to a single one, which is moreover somewhat displaced in frequency [42]. This problem is cured when a cumulant form is used instead of the GW self-energy [43], and much recent effort has been spent to work out high-energy spectral functions within a GW-based cumulant approach for different materials [44,45,46,47].…”

Section: Electron-plasmon Hamiltonians From First Principlesmentioning

confidence: 99%

Electronic polarons, cumulants and doubly dynamical mean field theory: Theoretical spectroscopy for correlated and less correlated materials

Biermann

Roekeghem

2016

Journal of Electron Spectroscopy and Related Phenomena

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The use of effective local Coulomb interactions that are dynamical, that is, frequencydependent, is an efficient tool to describe the effect of long-range Coulomb interactions and screening thereof in solids. The dynamical character of the interaction introduces the coupling to screening degrees of freedom such as plasmons or particle-hole excitations into the many-body description. We summarize recent progress using these concepts, putting emphasis on dynamical mean field theory (DMFT) calculations with dynamical interactions ("doubly dynamical mean field theory"). We discuss the relation to the combined GW+DMFT method and its simplified version "Screened Exchange DMFT", as well as the cumulant schemes of many-body perturbation theory. On the example of the simple transition metal SrVO 3 , we illustrate the mechanism of the appearance of plasmonic satellite structures in the spectral properties, and discuss implications for the low-energy electronic structure. Theoretical Spectroscopy: from many-body perturbation theory to dynamical Hubbard interactionsDetermining the behavior of a single electron in a periodic potential, created for example by the ions in a cristalline solid, is a textbook exercise of quantum mechanics. Determining the wave function of all the electrons in the solid, however, is an intractable many-body problem. The Pauli principle imposes full antisymmetry under exchange of any two electrons to this object, and electronic Coulomb interactions prevent it from being a simple Slater determinant.The good news is that in practice the knowledge of the full many-body wave function of the inhomogeneous electron gas in the solid is barely necessary: the relevant electronic properties are determined by the low-energy response to external perturbations, and the knowledge of these low-energy excitations requires much less information than the full ground-state wave function. In this sense, solid state spectroscopies are a most efficient means for characterizing the properties of a solid state system. An important example are photoemission experimentsangle-resolved or angle-integrated -where information about the electron removal and addition spectra are obtained. Within the simplest possible model for the photoemission process, the so-called "three-step model", the photocurrent can be expressed in terms of the one-particle spectral function A(k, ω) = − 1 π T r G(k, ω), and computing this quantity from first principles, that is, without adjustable parameters, is one of the central challenges of modern theoretical spectroscopy.Important progress has been achieved over the last decades within many-body perturbation theory: a first order expansion of the many-body self-energy Σ in the screened Coulomb interaction W [1, 2] leads to a conceptually simple approximation Σ = iGW which can be calculated within realistic electronic structure codes based on density functional theory (DFT). For reviews of 1 arXiv:1512.08499v1 [cond-mat.str-el]

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Real-time cumulant approach for charge-transfer satellites in x-ray photoemission spectra

Cited by 46 publications

References 45 publications

Finite Temperature Green’s Function Approach for Excited State and Thermodynamic Properties of Cool to Warm Dense Matter

Finite Temperature Green’s Function Approach for Excited State and Thermodynamic Properties of Cool to Warm Dense Matter

Particle-hole cumulant approach for inelastic losses in x-ray spectra

Electronic polarons, cumulants and doubly dynamical mean field theory: Theoretical spectroscopy for correlated and less correlated materials

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