Abstract
In nanoelectronics, transient dynamics is one of the key issues to characterize the performance of nanodevices. Based on the framework of the density functional theory (DFT), we studied the transient heat current and transient spin transfer torque (STT) using the nonequilibrium Green's function (NEGF) and the complex absorbing potential (CAP).
For the transient heat current, an exact time-dependent NEGF-DFT formalism to study the transient heat current under a step-like pulse of gate voltage is proposed beyond the wide-band limit. In order to speed up the calculation, an algorithm using the CAP is then developed. After replacing the Hamiltonian of leads by the CAP, the effective self-energy of the Green's function becomes energy-independent. The triple energy integration in the exact solution of transient heat current can then be reduced to a single energy integral which dramatically reduces the computational complexity. As an example, the NEGF-DFT-CAP formalism is applied to calculate the transient heat current under an upward gate voltage pulse for the Di-thiol benzene molecule connected by two semi-infinite aluminum leads.
The transient STT of the magnetic layered system is also investigated under the NEGF-DFT-CAP framework. In order to further increase the computational speed, the Pade approximation is introduced to replace the Fermi distribution function. Therefore, the energy integrals in the formalism of transient STT, including that of the Fermi distribution function, can be analytically calculated by the theorem of residue. As an application, the transient current-induced STT of Co/Cu/Co trilayers under an upward pulse of bias is studied.