First-principles investigation of transient current in molecular devices by using complex absorbing potentials

Based on the nonequilibrium Green's function (NEGF) coupled with density function theory (DFT), namely, NEGF-DFT quantum transport theory, we propose an efficient formalism to calculate the transient current of molecular devices under a step-like pulse from first principles. By combining NEGF-DFT with the complex absorbing potential (CAP), the computational complexity of our formalism (NEGF-DFT-CAP) is proportional to O(N) where N is the number of time steps in the time-dependent transient current calculation. Compared with the state-of-the-art algorithm of first-principles time-dependent calculation that scales with at least N-2, this order N technique drastically reduces the computational burden making it possible to tackle realistic molecular devices. We have presented a detailed discussion on how to implement this scheme numerically from first principles. To check the accuracy of our method, we carry out the benchmark calculation compared with NEGF-DFT formalism and they agree well with each other. As an application of this method, we investigate the transient current of a molecular device Al-C-3-Al from first principles.