Theoretical study of charge transport in molecular junctions
Date Issued
2015
Date
2015
Author(s)
Chang, Yao-Wen
Abstract
Charge transport processes in molecular junctions are studied theoretically by combining closed-time path (CTP) formalism, nonequilibrium Green’s function (NEGF), and renormalized perturbation theory. The molecular-junction Hamiltonian is mapped and partitioned into a collection of independent single-impurity Anderson’s Hamiltonians, which are treated as the zeroth-order Hamiltonian and are seen as the channels or orbitals that charge tunneling through or occupying, and the interactions between the channels are treated as perturbation. The quasi-particle concept is introduced to describe the kinetic processes. The electron density distribution of each orbital out of equilibrium can be given by solving a quasi-particle rate equation, and then the electric current can be known. By this method, we can study the charge transport processes with both the coherent tunneling and Coulomb blockade being considered. The present formalism is applied to the study of Coulomb inter- action on charge transport processes of few sites systems. Various nonlinear current responses, included Coulomb blockade gap, negative differential resistance (NDR), rectification, and current hysteresis, are ascribed and explained in test calculations. Except the model calculation, we have also use the present theory to a real system. Numerical calculations based on renormalized perturbation theory and Pariser-Parr-Pople (PPP) Hamiltonian are performed, and the effects of electron correlations are included by perturbative treatments of second-Born self-energies and GW self-energies. The current-voltage characteristics of the molecular junctions using benzene and butadiene as bridges are studied and discussed.
Subjects
molecular junctions
Type
thesis
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