  We propose an efficient computational method for evaluating the self-energy
matrices of electrodes to study ballistic electron transport properties in
nanoscale systems. To reduce the high computational cost incurred in large
systems, a contour integral eigensolver based on the Sakurai-Sugiura method
combined with the shifted biconjugate gradient method is developed to solve
exponential-type eigenvalue problem for complex wave vectors. A remarkable
feature of the proposed algorithm is that the numerical procedure is very
similar to that of conventional band structure calculations. We implement the
developed method in the framework of the real-space higher-order finite
difference scheme with nonlocal pseudopotentials. Numerical tests for a wide
variety of materials validate the robustness, accuracy, and efficiency of the
proposed method. As an illustration of the method, we present the electron
transport property of the free-standing silicene with the line defect
originating from the reversed buckled phases.
