An integrated piecewise thermal equilibrium approach based on the first-principles calculation method has been developed to calculate bias dependent electronic structures and current-and differential conductance-voltage characteristics of the gold-benzene-1,4-dithiol-gold molecular junction. The calculated currents and differential conductance have the same order of magnitude as experimental ones. An electron transfer was found between the two electrodes when a bias is applied, which renders the two electrodes to have different local electronic structures. It was also found that when Au 5d electrons were treated as core electrons the calculated currents were overestimated, which can be understood as an underestimate of the Au-S covalent bonding and consequently the contact potential barrier and the replacement of delocalized Au 5d carriers by more itinerant delocalized Au 6sp carriers in the electrodes.

Using the first-principles density functional theory calculations, we investigate the mechanical and electronic properties of biaxially strained graphitic carbon nitride (g-C 3 N 4 ). The results show highly isotropic mechanical properties and large linear elasticity of g-C 3 N 4 . Moreover, both the Perdew-Burke-Ernzehof (PBE) and Heyd-Scuseria-Ernzerhof (HSE06) band gaps reach the maximum values at 10% strain. The bonding properties are analyzed based on the electronic localization function (ELF). In addition, the photon transition between band gap is weak, suggesting the monolayer g-C 3 N 4 is not suitable for a solar cell material. Enough biaxial strain can induce the spin splitting of g-C 3 N 4 , and it is found that the spin-unrestricted band gap of g-C 3 N 4 can be overestimated. This work provides valuable insights for designing the new elastic electronic and spintronic devices based on two-dimensional g-C 3 N 4 .

A nanometer-scale Au/Al(0001)/Au junction has been studied by first-principles calculation methods. The calculated current density-voltage curve shows Ohmic behavior, switching effect, and negative differential conductance in various bias ranges. The electronic structure shows the existence of an intrinsic band tilt due to the polar nature of the AlN film, which gives rise to the presence of hole states at the N-surface side and interface states at the Al-surface side of the AlN film. The bias induced changes of hole and interface states and the states of the Al and N ions in central layers determine the transport property.