Many-body Green's function theory for electron-phonon interactions: Ground state properties of the Holstein dimer

被引:17
作者
Sakkinen, Niko [1 ]
Peng, Yang [2 ,3 ,4 ]
Appel, Heiko [4 ]
van Leeuwen, Robert [1 ]
机构
[1] Univ Jyvaskyla, Nanosci Ctr, Dept Phys, Survontie 9, Jyvaskyla 40014, Finland
[2] Free Univ Berlin, Dahlem Ctr Complex Quantum Syst, D-14195 Berlin, Germany
[3] Free Univ Berlin, Fachbereich Phys, D-14195 Berlin, Germany
[4] Max Planck Gesell, Fritz Haber Inst, D-14195 Berlin, Germany
基金
芬兰科学院;
关键词
DYNAMICAL PROPERTIES; LATTICE-VIBRATIONS; POLARON; MODEL; APPROXIMATIONS;
D O I
10.1063/1.4936142
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
We study ground-state properties of a two-site, two-electron Holstein model describing two molecules coupled indirectly via electron-phonon interaction by using both exact diagonalization and self-consistent diagrammatic many-body perturbation theory. The Hartree and self-consistent Born approximations used in the present work are studied at different levels of self-consistency. The governing equations are shown to exhibit multiple solutions when the electron-phonon interaction is sufficiently strong, whereas at smaller interactions, only a single solution is found. The additional solutions at larger electron-phonon couplings correspond to symmetry-broken states with inhomogeneous electron densities. A comparison to exact results indicates that this symmetry breaking is strongly correlated with the formation of a bipolaron state in which the two electrons prefer to reside on the same molecule. The results further show that the Hartree and partially self-consistent Born solutions obtained by enforcing symmetry do not compare well with exact energetics, while the fully self-consistent Born approximation improves the qualitative and quantitative agreement with exact results in the same symmetric case. This together with a presented natural occupation number analysis supports the conclusion that the fully self-consistent approximation describes partially the bipolaron crossover. These results contribute to better understanding how these approximations cope with the strong localizing effect of the electron-phonon interaction. (C) 2015 AIP Publishing LLC.
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页数:19
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