Conserving Approximations in Nonequilibrium Green Function Theory
نویسندگان
چکیده
In this chapter we introduce the fundamental concepts behind the Green Function Theory. We start from a description of the second quantization method and then, after introducing the ensemble average of an operator, we define the main object of the theory, the Green function. Further on, after obtaining the equation of motion for the Green function, we introduce the self-energy operator and we discuss the Hartree-Fock approximation, the second-Born approximation and the GW approximation to the self-energy.
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