Abstract

The method of many-body Green's functions is developed for arbitrary systems of electrons and nuclei starting from the full (beyond Born-Oppenheimer) Hamiltonian of Coulomb interactions and kinetic energies. The theory presented here resolves the problems arising from the translational and rotational invariance of this Hamiltonian that afflict the existing many-body Green's function theories. We derive a coupled set of exact equations for the electronic and nuclear Green's functions and provide a systematic way to approximately compute the properties of arbitrary many-body systems of electrons and nuclei beyond the Born-Oppenheimer approximation. The case of crystalline solids is discussed in detail.

Highlights

  • The Born-Oppenheimer (BO) approximation [1,2] is among the most fundamental ingredients of modern condensed-matter theory

  • The BO approximation makes calculations computationally feasible, the motion of nuclear wave packets in the lowest BO potential energy surface provides us with an intuitive picture of many chemical reactions

  • The total wave function of the system is a single product of a nuclear wave function and the many-electron wave function which parametrically depends on the nuclear coordinates

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Summary

INTRODUCTION

The Born-Oppenheimer (BO) approximation [1,2] is among the most fundamental ingredients of modern condensed-matter theory. In this article we follow the first option: Our goal is to develop a Green’s function-based many-body theory for the complete system of electrons and nuclei where the Green’s functions are defined in terms of coordinates that refer to a body-fixed coordinate frame. First steps in this direction were taken with the formulation of a multicomponent density-functional theory [54,55,56] and with the derivation of a Green’s-function framework [57].

Hamiltonian
Euler angles
EQUATION OF MOTION FOR THE ELECTRONIC GREEN’S FUNCTION
EQUATION OF MOTION FOR THE NUCLEAR GREEN’S FUNCTION
HEDIN’S EQUATIONS
CHOICE OF REFERENCE POSITIONS
Nuclear vibrations
Nuclear self-energy
VIII. CRYSTALLINE SOLIDS
Phonons and their interactions
Momentum functions
CONCLUSIONS

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