Abstract:
With the development of nanotechnology, intensive research interest has been centered on the electronic transport properties of nano-scale devices and several theoretical formalisms are developed to study coherent transport problems. In the past half century, Kohn-Sham density functional theory (KS-DFT) has become the standard technique of first-principle calculation method in condensed matter physics. Despite its accuracy, its orbital-based nature limits its application on large-scale system and the order N-cube algorithm is time-consuming. On the other hand, orbital-free DFT (OF-DFT) involves no wave function or electron orbital. Hence OF-DFT has its advantages in linear scaling and fast and stable convergence in numerical calculation.
In this thesis, the orbital-free density functional theory (OFDFT) plus non-equilibrium Green's function (NEGF) formalism is developed to simulate first principal electronic transport in atomic systems. OF-DFT is adopted to self-consistently obtain the effective potential of the investigated system. Then the Hamiltonian of this system is constructed on LCAO (linear combination of atomic orbital) basis. Finally, Green’s function is calculated from the Hamiltonian. The formalism is applied on a silicon nanostructure. Numerical results show that, the method could qualitatively predict characteristics of the system but generally it is less accurate than the orbital-dependent methods. The advantages of this method lie in the low numerical cost which is critical on modeling realistic devices. Upon progresses made to improve its accuracy, the OFDFT plus NEGF formalism could play an important role in transport study of large-scale atomic systems.