Speaker: Dr. Ri-Ping Wang, Beijing Computational Science Research Center

Abstract: This study designs the algorithm for the newly-proposed phonon approach used to simulate the electronic excitation dynamics in condensed matters. The phonon approach treats the static configuration of electron–nuclear geometry as an open system, and describes the lattice vibration as phonon field in impose the environment-like perturbations on it in a way analogous to the external influence of electromagnetic field. The phonon field results in the relaxation of hot electrons, which have been excited to high-energy state of the static nuclear geometry by absorbing photons. The relaxation dynamics of the electronic hopping is governed by the nonadiabatic Hamiltonian and propagates along the time-dependent Schr¨odinger equation. The nonadiabatic Hamiltonian is constructed by accounting for the details of the electron–phonon interactions and also evolves along time. The phonon approach proposed in this way is expected be much faster than the traditional approach, the nonadiabatic molecular dynamics simulation (NAMD). Because of this, it possibly creates the starting point for simulating the electronic excitation dynamics for large systems, large number of hot electrons, and long evolution time, each of which is currently basically unaffordable with NAMD. Another characteristic capability unreachable by NAMD is that the phonon approach decomposes the overall excitation dynamics based onto the detailed contributions from individual phonon modes, explicitly revealing the function of each specific phonon mode, and therefore it opens the age of engineering the excitation dynamics with considerable hidden potentiality for applications. Since the phonon perturbation is also the driving force for the spacial diffusion of electrons, the phonon approach allows the coupling between excitation dynamics in spectral space and charge transport in spacial space, paving the way to a unified method of simulating charge transport accounting for the hot electrons. The phonon approach builds up the framework for conveniently including the effect of the electron–photon interactions by absorbing the well-studied dipole transition moment, therefore, it looks forward to a full map of excitation dynamics simulation based on electron–phonon–photon interactions. This presentation focuses on the key steps of algorithm design, with a bit of prospects on software development and potential applications.

Date&Time: December 19, 2014 (Friday), 14:30–15:30
Location: 606 Conference Room