Complex absorbing potential based Lorentzian fitting scheme and time dependent quantum transport

Based on the complex absorbing potential (CAP) method, a Lorentzian expansion scheme is developed to express the self-energy. The CAP-based Lorentzian expansion of self-energy is employed to solve efficiently the Liouville-von Neumann equation of one-electron density matrix. The resulting method is applicable for both tight-binding and first-principles models, and is used to simulate the transient currents through graphene nanoribbons and a benzene molecule sandwiched between two carbon-atom-chains.Comment: This paper is about a methodology development on the time dependent quantum transport theory. It has 22 pages and 6 figure

Time-dependent quantum transport: An efficient method based on Liouville-von-Neumann equation for single-electron density matrix

Basing on our hierarchical equations of motion for time-dependent quantum transport [X. Zheng, G. H. Chen, Y. Mo, S. K. Koo, H. Tian, C. Y. Yam, and Y. J. Yan, J. Chem. Phys. 133, 114101 (2010)], we develop an efficient and accurate numerical algorithm to solve the Liouville-von-Neumann equation. We solve the real-time evolution of the reduced single-electron density matrix at the tight-binding level. Calculations are carried out to simulate the transient current through a linear chain of atoms, with each represented by a single orbital. The self-energy matrix is expanded in terms of multiple Lorentzian functions, and the Fermi distribution function is evaluated via the Pade spectrum decomposition. This Lorentzian-Pade decomposition scheme is employed to simulate the transient current. With sufficient Lorentzian functions used to fit the self-energy matrices, we show that the lead spectral function and the dynamics response can be treated accurately. Compared to the conventional master equation approaches, our method is much more efficient as the computational time scales cubically with the system size and linearly with the simulation time. As a result, the simulations of the transient currents through systems containing up to one hundred of atoms have been carried out. As density functional theory is also an effective one-particle theory, the Lorentzian-Pade decomposition scheme developed here can be generalized for first-principles simulation of realistic systems. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737864

Can Molecular Quantum Interference Effect Transistors Survive Vibration?

Quantum interference in cross-conjugated molecules can be utilized to construct molecular quantum interference effect transistors. However, whether its application can be achieved depends on the survivability of the quantum interference under real conditions such as nuclear vibration. We use two simulation methods to investigate the effects of nuclear vibration on quantum interference in a meta-linked benzene system. The simulation results suggest that the quantum interference is robust against nuclear vibration not only in the steady state but also in its transient dynamics, and thus the molecular quantum interference effect transistors can be realized

Enhanced Photovoltaic Properties Induced by Ferroelectric Domain Structures in Organometallic Halide Perovskites

Organometallic halide perovskites have drawn substantial interest due to their outstanding performance in solar energy conversion and optoelectronic applications. The presence of ferroelectric domain walls in these materials has shown to have a profound effect on their electronic structure. Here, we use a density-functional-based tight-binding model, coupled to nonequilibrium Green’s function method, to investigate the effects of ferroelectric domain walls on electronic transport properties and charge carrier recombination in methylammonium lead–iodide perovskite, MAPbI3. With the presence of ferroelectric domain walls, segregation of transport channels for electrons and holes is observed, and the conductance of perovskites is substantially increased due to the reduced band gap. In addition, by taking into account interactions with photons in the vacuum environment, it is found that electron–hole recombination in perovskites with ferroelectric domain walls is drastically suppressed due to the segregation of carrier transport paths, which could enhance photovoltaic performance