Within the exact framework established recently, which is a successful marriage
between the time dependent density functional theory for open electronic system
and quantum dissipation theory formulated in the hierarchical equations of motion,
an entirely new scheme is proposed in this thesis to simulate the time-dependent
quantum transport in nano-devices at both zero and finite temperature equally
without relying on the pole structure of the Fermi distribution function. Neither
does it depend on any non-unique parametrization of the line-width matrix, hence,
this new practical approach can be integrated with the first principles simulations
seamlessly.
Beyond the exact framework, a reliable method which works under the Wide-
Band-Limit approximation at zero temperature is also developed. At the price of
loss of some non-Markovian memory effects on the dynamics, a set of equations
of motion which terminates at the first tier instead of the second tier is obtained.
Benefiting from the latest advancement of numerical analysis, a hybrid fourth-order
Runge-Kutta algorithm is proposed to solve this set of equations of motion which
comprises stiff ones. Based on this result, an alternative scheme is considered to
deal with the same approximation at finite temperature.
As an illustration of these new approaches, the transient current of the one
dimensional tight-binding periodical chain with and without a single impurity, driven
by some time alternating and/or static bias voltages, are investigated. The influence
of temperature and switch-on rate of bias voltage is exemplified. Particularly, in the
one dimensional tight-binding chain with a single impurity which breaks its perfect
periodicity, an asymmetry between the left and right transient current is found.
Comparison between the results under the Wide-Band-Limit approximation and
those with the exact description is carried out. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/183325 |
| Date | January 2012 |
| Creators | Tian, Heng, 田恒 |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B47869446 |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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