Conserving approximations in nonequilibrium green function theory

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The subject of this thesis lies in the field of many-body theory. This field emerged from the aim to understand the behavior and characterize the properties of many-body systems. When the systems considered are large, the interactions between the elementary constituents of these systems can construct phenomena which may be very different from the behavior of the constituents considered as separated. In an attempt to describe these large systems, these very interactions complicate the description far beyond the computational possibilities. In order to study the collective behavior of the interacting elementary constituents, the complexity of the interaction between them calls for simplifications. All physical approximations made in order to advance in understanding the behavior of many-body systems constitute the field of many-body physics. Within the field of many-body physics, the Green Function Theory describes the behavior and the properties of a system with the aid of an object called the Green function. The Green function is the probability amplitude of finding a particle that has been inserted in the system at (r′, t′) and removed at (r, t). Since between addition and removal the particle propagated through the system interacting with all other particles, the Green function contains information about its properties. In the Green Function Theory, the interactions of an electronic system i.e. the effects of exchange and correlation, are incorporated into the so called self-energy operator. There are different possible approximations of the self-energy and they completely determine the properties of the system. One of the most widely used approximations of the self-energy is the GW approximation. In this approximation, the self-energy operator is the product of the Green function that describes the propagation of particles and holes in the system, and the dynamically screened interaction which describes how the bare interaction between electrons is modified due to the presence of the other electrons.

	Titlepages
	Contents
	Chapter 1
	Chapter 2
	Chapter 3
	Chapter 4
	Chapter 5
	Chapter 6
	Chapter
	Appendices
	References
	Epilogue
	Samenvatting
	Rezumat
	List of publications
	Complete thesis
	Stellingen

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