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Jun 30, 2018
06/18

by
G. Stefanucci; Y. Pavlyukh; A. -M. Uimonen; R. van Leeuwen

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We present a diagrammatic approach to construct self-energy approximations within many-body perturbation theory with positive spectral properties. The method cures the problem of negative spectral functions which arises from a straightforward inclusion of vertex diagrams beyond the GW approximation. Our approach consists of a two-steps procedure: we first express the approximate many-body self-energy as a product of half-diagrams and then identify the minimal number of half-diagrams to add in...

Topics: Other Condensed Matter, Condensed Matter

Source: http://arxiv.org/abs/1408.6163

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12

Jun 28, 2018
06/18

by
E. Perfetto; A. -M. Uimonen; R. van Leeuwen; G. Stefanucci

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We put forward a first-principle NonEquilibrium Green's Function (NEGF) approach to calculate the transient photoabsorption spectrum of optically thin samples. The method can deal with pump fields of arbitrary strength, frequency and duration as well as for overlapping and nonoverlapping pump and probe pulses. The electron-electron repulsion is accounted for by the correlation self-energy, and the resulting numerical scheme deals with matrices that scale quadratically with the system size. Two...

Topics: Mesoscale and Nanoscale Physics, Atomic Physics, Physics, Condensed Matter

Source: http://arxiv.org/abs/1507.05590

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4.0

Jun 29, 2018
06/18

by
Y. Pavlyukh; A. -M. Uimonen; G. Stefanucci; R. van Leeuwen

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We present a systematic study of vertex corrections in the homogeneous electron gas at metallic densities. The vertex diagrams are built using a recently proposed positive-definite diagrammatic expansion for the spectral function. The vertex function not only provides corrections to the well known plasmon and particle-hole scatterings, but also gives rise to new physical processes such as generation of two plasmon excitations or the decay of the one-particle state into a two-particles-one-hole...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1607.04309

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36

Sep 21, 2013
09/13

by
D. Koudela; A. -M. Uimonen; H. Häkkinen

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We study the dependence of the intrinsic conductance of a nanocontact on its shape by using the recursion-transfer-matrix method. Hour-glass, torus, and spherical shapes are defined through analytic potentials, the latter two serving as rough models for ring-like and spherical molecules, respectively. The sensitivity of the conductance to geometric details is analyzed and discussed. Strong resonance effects are found for a spherical contact weakly coupled to electron reservoirs.

Source: http://arxiv.org/abs/0808.3670v1

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110

Jul 20, 2013
07/13

by
A. -M. Uimonen; E. Khosravi; A. Stan; G. Stefanucci; S. Kurth; R. van Leeuwen; E. K. U. Gross

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We study time-dependent electron transport through an Anderson model. The electronic interactions on the impurity site are included via the self-energy approximations at Hartree-Fock (HF), second Born (2B), GW, and T-Matrix level as well as within a time-dependent density functional (TDDFT) scheme based on the adiabatic Bethe-Ansatz local density approximation (ABALDA) for the exchange correlation potential. The Anderson model is driven out of equilibrium by applying a bias to the leads and its...

Source: http://arxiv.org/abs/1107.0162v2

12
12

Jun 27, 2018
06/18

by
A. -M. Uimonen; G. Stefanucci; Y. Pavlyukh; R. van Leeuwen

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In a recent paper [Phys. Rev. B 90, 115134 (2014)] we put forward a diagrammatic expansion for the self-energy which guarantees the positivity of the spectral function. In this work we extend the theory to the density response function. We write the generic diagram for the density-response spectrum as the sum of partitions. In a partition the original diagram is evaluated using time-ordered Green's functions (GF) on the left-half of the diagram, antitime-ordered GF on the right-half of the...

Topics: Other Condensed Matter, Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1503.02158

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44

Sep 21, 2013
09/13

by
A. -M. Uimonen; E. Khosravi; G. Stefanucci; S. Kurth; R. van Leeuwen; E. K. U. Gross

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We study transport through an interacting model system consisting of a central correlated site coupled to finite bandwidth tight-binding leads, which are considered as effectively noninteracting. Its nonequilibrium properties are determined by real-time propagation of the Kadanoff-Baym equations after applying a bias voltage to the system. The electronic interactions on the central site are incorporated by means of self-energy approximations at Hartree-Fock, second Born and GW level. We...

Source: http://arxiv.org/abs/1106.5631v1

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84

Sep 24, 2013
09/13

by
E. Khosravi; A. -M. Uimonen; A. Stan; G. Stefanucci; S. Kurth; R. van Leeuwen; E. K. U. Gross

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The possibility of finding multistability in the density and current of an interacting nanoscale junction coupled to semi-infinite leads is studied at various levels of approximation. The system is driven out of equilibrium by an external bias and the non-equilibrium properties are determined by real-time propagation using both time-dependent density functional theory (TDDFT) and many-body perturbation theory (MBPT). In TDDFT the exchange-correlation effects are described within a recently...

Source: http://arxiv.org/abs/1112.2871v1