Application of hierarchical equations of motion to time dependent quantum transport
Heng Tian
Abstract
Within the exact framework established recently, which is a successful marriage\n\nbetween the time dependent density functional theory for open electronic system\n\nand quantum dissipation theory formulated in the hierarchical equations of motion,\n\nan entirely new scheme is proposed in this thesis to simulate the time-dependent\n\nquantum transport in nano-devices at both zero and finite temperature equally\n\nwithout relying on the pole structure of the Fermi distribution function. Neither\n\ndoes it depend on any non-unique parametrization of the line-width matrix, hence,\n\nthis new practical approach can be integrated with the first principles simulations\n\nseamlessly.\n\nBeyond the exact framework, a reliable method which works under the Wide-\n\nBand-Limit approximation at zero temperature is also developed. At the price of\n\nloss of some non-Markovian memory effects on the dynamics, a set of equations\n\nof motion which terminates at the first tier instead of the second tier is obtained.\n\nBenefiting from the latest advancement of numerical analysis, a hybrid fourth-order\n\nRunge-Kutta algorithm is proposed to solve this set of equations of motion which\n\ncomprises stiff ones. Based on this result, an alternative scheme is considered to\n\ndeal with the same approximation at finite temperature.\n\nAs an illustration of these new approaches, the transient current of the one\n\ndimensional tight-binding periodical chain with and without a single impurity, driven\n\nby some time alternating and/or static bias voltages, are investigated. The influence\n\nof temperature and switch-on rate of bias voltage is exemplified. Particularly, in the\n\none dimensional tight-binding chain with a single impurity which breaks its perfect\n\nperiodicity, an asymmetry between the left and right transient current is found.\n\nComparison between the results under the Wide-Band-Limit approximation and\n\nthose with the exact description is carried out.