SAKE: first-principles electron transport calculation code

Abstract

We developed and implemented a numerical code called SAKE, which stands for (simulation code for atomistic Kohn–Sham equation). We developed it for first-principle electron transport calculations based on density-functional theory and non-equilibrium Green’s function formalism. First, we present the central calculation parts of the formalism of the electronic states and transport properties for open and non-equilibrium systems. We show specific computational techniques, such as the use of a complex contour integration for charge density from the density matrix, which is compared with the calculation method of summing the residues of the Fermi-Dirac distribution, as well as the efficient achievement of the self-consistent procedures. Thereafter, for applications of the present computation code, SAKE, we present first-principle calculation results of three different systems. We first analyze electronic structures of polythiophene molecular wires, compare summation techniques for the density matrix. We show thermoelectric properties of an n-type antiferromagnetic semiconductor CuFeS2 as a second application. The electrical conductance, electrical thermal conductance, and the Seebeck coefficients with carrier doping are examined, and the analytical form of the Seebeck coefficient is briefly described. For the third application, we analyze the electron transport properties of polyaniline molecular wires under structural deformations, i.e. rotations around the transport direction. The thermally averaged current-voltage characteristics are also analyzed. The results show that the current decreases as the temperature increases which are determined based on the competition between the thermal energy and the electronic energy, which increases with the rotation angle.