The real-time electronic dynamics on material surfaces is critically important to a variety of applications. However, their simulations have remained challenging for conventional methods such as the time-dependent density-functional theory (TDDFT) for isolated and periodic systems. By extending the applicability of TDDFT to systems with open boundaries, we achieve accurate atomistic simulations of real-time electronic response to local perturbations on material surfaces. Two prototypical scenarios are exemplified: the relaxation of an excess electron on graphene surface, and the electron transfer across the molecule-graphene interface. Both the transient and long-time asymptotic dynamics are validated, which accentuates the fundamental importance and unique usefulness of an open-system TDDFT approach. The simulations also provide insights into the characteristic features of temporal electron evolution and dissipation on surfaces of bulk materials.PACS numbers: 71.15. Mb, 73.20.Mf, 72.80.Vp How electrons evolve at the surfaces or interfaces of materials is fundamentally significant to a variety of applications, including photovoltaics, nanoelectronics, heterogeneous catalysis, etc. Consider a prototypical system that a molecule is adsorbed on a surface of a material. For instance, in a dye-sensitized solar cell [1], photo-excited electrons transfer from the dye molecule to the semiconductor surface, and then drain into the bulk [2]. In a biomimetic water-splitting complex, a catalytic molecule acquires electrons by oxidation of water and then feeds them into the supporting conductor [3]. Apparently, for these systems the real-time electronic processes on material surfaces are crucially important to their functionality. Accurate simulations at atomic level will be very helpful for understanding the key features of the real-time electronic dynamics and the underlying mechanisms.Considering the size and complexity of a system involving material surface, the time-dependent densityfunctional theory (TDDFT) [4][5][6][7] is potentially suitable for carrying out the theoretical studies, due to its favorable balance between accuracy and efficiency.For any practical application of TDDFT, a boundary condition exists explicitly or implicitly. So far the success of TDDFT has been largely restricted to isolated and periodic boundary conditions. For isolated systems (atoms, molecules, clusters, etc.) the electron density falls off to zero at infinite distance, while for periodic systems (polymers, crystals, etc.) the electron density possesses the lattice translational invariance symmetry. It is worth pointing out that, although TDDFT has been employed to study excited-state properties (such as absorption and electron-energy-loss spectra) of periodic solids [8][9][10][11], a rigorous proof justifying the existence of a TDDFT for periodic systems is still lacking [12][13][14].Apparently, for a composite system where a molecule is adsorbed on a material surface, neither an isolated nor a periodic model is suitable, particularl...

Understanding of the electroluminescence (EL) mechanism in optoelectronic devices is imperative for further optimization of their efficiency and effectiveness. Here, a quantum mechanical approach is formulated for modeling the EL processes in nanoscale light emitting diodes (LED). Based on non-equilibrium Green's function quantum transport equations, interactions with the electromagnetic vacuum environment are included to describe electrically driven light emission in the devices. The presented framework is illustrated by numerical simulations of a silicon nanowire LED device. EL spectra of the nanowire device under different bias voltages are obtained and, more importantly, the radiation pattern and polarization of optical emission can be determined using the current approach. This work is an important step forward towards atomistic quantum mechanical modeling of the electrically induced optical response in nanoscale systems.

Environmental effects play an important role on the electron dynamics of open systems, which provide channels for dissipation of electrons and energy in the systems. However, accurate description of the environment of quantum systems is still challenging. The environment is usually assumed to be a quasi-one-dimensional reservoir in previous theoretical studies. In this work, we focus on systems that are adsorbed on bulk surfaces. Two different approaches to describe the spectral details of the environment are adopted and compared: the Lorentzian decomposition approach and the complex absorbing potential (CAP) approach. To achieve similar accuracy for the spectral density of the environment, it is shown that the Lorentzian decomposition approach is computationally more efficient than the CAP approach, especially for bulk systems. The electron dynamics is then followed using the nonequilibrium Green’s function method for two systems: a modeling bulk surface system and a scanning tunneling microscope junction. Dissipation paths of excited charge carriers can be analyzed, which provide insights into the understanding of excitation dynamics in bulk materials.