Chapter 5 - Quantum Correlation Effects in Electron Dynamics in Molecular Wires and Solar Cells: The Nonequilibrium Green's Function Approach

Abstract

Abstract In the development of different quantum chemical computational methods the main attention is paid to solving stationary many-body Schrodinger equations. Recent developments in chemistry, physics, energy physics, and materials science have brought forth a new class of problems where the evolution of a system is considered. As in the stationary case correlation effects are also important in the correct description of time-dependent problems. The most rigorous approach to describe system evolution is based on nonequilibrium Green's functions (or Keldysh functions). In chapter 2 we provide a general description of some important properties of nonequilibrium Green's functions. In particular we introduce nonequilibrium Green's functions on a Keldysh contour, describe the projection technique, and derive Kadanoff-Baym equations. The application of nonequilibrium Green's functions to tunneling junctions is given in chapter 3 . In this chapter the equation for electric current is presented and Dyson equations for different nonequilibrium Green's functions are derived. As the implementation of the proposed methods, the particular numerical calculations of electric current in molecular diodes and transistors are discussed. We also describe the application of Keldysh functions to the calculations of photoelectric current in quantum dot sensitized solar cells. The general equation for photocurrent is expressed in terms of nonequilibrium Green's functions, which can be found from the proper Dyson equations. These equations contain arbitrary time-dependent electric field in the dipole approximation. The importance of the application of nonequilibrium Green's functions to various time-dependent problems is emphasized in conclusions.