First-principles study of the effects of the electrode-molecule contact configurations on the molecule diode device characteristics

Abstract

Though density functional theory (DFT)-based non-equilibrium Green’s function (NEGF) formalism has been considered as the most general and powerful tools in terms of describing non-equilibrium state, it suffers from several short comings. In this thesis, we improve and verify our recently developed method based on a microcanonical picture that maps steady-state non-equilbrium statistics to drain-to-source excitation named multispace constrained density functional theory (MS-DFT). We heuristically settle the electron occupation rule for the non-equilibrium channel states by the excellent accordance between MS-DFT and DFT-NEGF results. Then, we study the correlations between the diode effects in single molecular junctions and the geometrical conformation of S–Au contact in which the atomistic understanding has been so far incomplete. We again carried out finite-bias first-principles quantum transport calculations based on MS-DFT with varying out the molecular core from insulating core to non-insulating one and find out the relationship between the rectification behavior of the junctions and the S–Au linkage coordination numbers.