Initial correlated states for the generalized Kadanoff–Baym Ansatz without adiabatic switching-on of interactions in closed systems

Hopjan, Miroslav; Verdozzi, Claudio

doi:10.1140/epjst/e2018-800054-3

Cited by 20 publications

(21 citation statements)

References 32 publications

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“…(9) by using a time-stepping algorithm [53,88]. While the inclusion of initial correlations has been shown to be possible also within GKBA [52,54,90,91], here we adiabatically switch on the many-particle interactions and only include the collision integral in the form of Eq. (10).…”

Section: B Time Propagation Of the Nonequilibrium Green's Functionsmentioning

confidence: 99%

“…We note in passing that the preparation step may consume a considerable amount of computational time [53], and it would be highly attractive to apply some sort of restart protocol, e.g., of Refs. [52,54,90,91], for a separate calculation starting at t = t 0 including the initially correlated state. However, we have found that numerous tests (not shown) for this procedure result in nonstationary behavior.…”

Section: A Driving With a Laser Pulsementioning

confidence: 99%

“…[33] by reducing the two-time propagation of the Green's function to the time propagation of a time-local density matrix via the generalized Kadanoff-Baym ansatz (GKBA), thereby reducing the computational scaling to the number of time steps squared. While this approach was acknowledged and used already in the 1990s [34][35][36][37][38], its recent revival [39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] has made it possible to combine the NEGF approach with ab initio descriptions of realistic atomic, molecular, and condensed matter systems [57][58][59][60][61]. Recent development has further allowed for an equivalent but more efficient representation of the GKBA time evolution with only a linear scaling in the number of time steps [62][63][64].…”

Section: Introductionmentioning

confidence: 99%

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Comparing the generalized Kadanoff-Baym ansatz with the full Kadanoff-Baym equations for an excitonic insulator out of equilibrium

Tuovinen¹,

Golež²,

Eckstein³

et al. 2020

Phys. Rev. B

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We investigate out-of-equilibrium dynamics in an excitonic insulator (EI) with a finite-momentum pairing perturbed by a laser-pulse excitation and a sudden coupling to fermionic baths. The transient dynamics of the excitonic order parameter is resolved using the full nonequilibrium Green's function approach and the generalized Kadanoff-Baym ansatz (GKBA) within the second-order Born approximation. The comparison between the two approaches after a laser-pulse excitation shows a good agreement in the weak and the intermediate photodoping regime. In contrast, the laser-pulse dynamics resolved by the GKBA does not show a complete melting of the excitonic order after a strong excitation. Instead we observe persistent oscillations of the excitonic order parameter with a predominant frequency given by the renormalized equilibrium band gap. This anomalous behavior can be overcome within the GKBA formalism by coupling to an external bath, which leads to a transition of the EI system toward the normal state. We analyze the long-time evolution of the system and distinguish decay timescales related to dephasing and thermalization.

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Section: B Time Propagation Of the Nonequilibrium Green's Functionsmentioning

confidence: 99%

Section: A Driving With a Laser Pulsementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Comparing the generalized Kadanoff-Baym ansatz with the full Kadanoff-Baym equations for an excitonic insulator out of equilibrium

Tuovinen¹,

Golež²,

Eckstein³

et al. 2020

Phys. Rev. B

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“…The correlated initial state therefore needs to be prepared by starting with an uncorrelated (or HF) system and slowly switching on the interaction (adiabatic switching procedure) [25,36,48,51]. However, the inclusion of the initial correlations has been shown to be possible also within GKBA [52][53][54].…”

Section: )mentioning

confidence: 99%

Efficient computation of the second-Born self-energy using tensor-contraction operations

Tuovinen

Covito

Sentef

2019

The Journal of Chemical Physics

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In the nonequilibrium Green's function approach, the approximation of the correlation self-energy at the second-Born level is of particular interest, since it allows for a maximal speed-up in computational scaling when used together with the Generalized Kadanoff-Baym Ansatz for the Green's function. The present day numerical time-propagation algorithms for the Green's function are able to tackle first principles simulations of atoms and molecules, but they are limited to relatively small systems due to unfavourable scaling of self-energy diagrams with respect to the basis size. We propose an efficient computation of the self-energy diagrams by using tensorcontraction operations to transform the internal summations into functions of external low-level linear algebra libraries. We discuss the achieved computational speed-up in transient electron dynamics in selected molecular systems.

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“…However, one of our longer term aims is to use our scheme (for skyrmions and other magnetic phenomena) in realistic materials. Based on our experience with double‐time NEGF, this is when correlations (even weak ones) do in fact play a role, and need to be accounted for via self‐energies contributions, determined, for example, via many‐body approximations. In this case, for large systems and many orbitals, double‐time NEGF can rapidly become computationally expensive, and simplified schemes can gain prominence.…”

Section: Introductionmentioning

confidence: 99%

Steering Magnetic Skyrmions with Currents: A Nonequilibrium Green's Functions Approach

Boström

Verdozzi

2019

Physica Status Solidi (b)

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Magnetic skyrmions, topologically protected vortex-like configurations in spin textures, are of wide conceptual and practical appeal, notably in relation to the making of so-called race-track memory devices. Skyrmions can be created, steered, and destroyed with magnetic fields and/or (spin) currents.Here the authors focus on the latter mechanism, analyzed via a microscopic treatment of the skyrmion-current interaction. The system considered is an isolated skyrmion in a square-lattice cluster, interacting with electron spins in a current-carrying quantum wire. For the theoretical description, a quantum formulation of spin-dependent currents via nonequilibrium Green's functions (NEGF) within the generalized Kadanoff-Baym ansatz (GKBA) is employed. This is combined with a treatment of skyrmions based on classical localized spins, with the skyrmion motion described via Ehrenfest dynamics. With the mixed quantum-classical scheme, the authors assess how time-dependent currents can affect the skyrmion dynamics, and how this in turn depends on electron-electron and spin-orbit interactions in the wire. This study shows the usefulness of a quantum-classical treatment of skyrmion steering via currents, as a way for example to validate/extract an effective, classical-only, description of skyrmion dynamics from a microscopic quantum modeling of the skyrmion-current interaction.

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Initial correlated states for the generalized Kadanoff–Baym Ansatz without adiabatic switching-on of interactions in closed systems

Cited by 20 publications

References 32 publications

Comparing the generalized Kadanoff-Baym ansatz with the full Kadanoff-Baym equations for an excitonic insulator out of equilibrium

Comparing the generalized Kadanoff-Baym ansatz with the full Kadanoff-Baym equations for an excitonic insulator out of equilibrium

Efficient computation of the second-Born self-energy using tensor-contraction operations

Steering Magnetic Skyrmions with Currents: A Nonequilibrium Green's Functions Approach

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