Algorithm advances and applications of time-dependent first-principles simulations for ultrafast dynamics

Far from equilibrium phenomenon is a central theme of contemporary material research. Such phenomenon can exhibit itself in atomic structure and dynamics, but very often it also happens as non-equilibrium phenomenon in the electronic structure. In ab initio material simulation, density functional theory (DFT) has played an essential role in studying electronic ground state problems. For excited states, besides many-body perturbation theory, another powerful tool is the time dependent DFT (TDDFT) method. In particular, the real-time TDDFT (rt-TDDFT) method can be used to simulate many non-equilibrium phenomena directly. Here we introduce our works on some algorithm advances based on our recently rt-TDDFT method. This method uses the plane-wave basis set, and significantly accelerates its efficiency by increasing the time step from 0.1-1 as in traditional methods to 0.2-0.5 fs. The noncollinear magnetic moments and spin-orbit coupling have also been included in our rt-TDDFT method. Furthermore, a Boltzmann-TDDFT algorithm has been developed to solve the hot carrier overheating problem in Ehrenfest dynamics, and a natural orbital branching algorithm has been developed to overcome the mean-field approximation in Ehrenfest dynamics nuclear trajectory, thus allows stochastic multiple paths in chemical reactions. Utilizing these methods, we have studied the photoinduced ultrafast demagnetization, ultrafast phase transition, energy transfer between plasmon and hot carriers, as well as the high-energy ion implantation and low-energy atomic diffusion in semiconductors. We believe the tools as the ones introduced here can enable us to study a wide range of phenomena which are of great interest in modern day material research. This article is categorized under: Structure and Mechanism > Computational Materials Science Electronic Structure Theory > Ab Initio Electronic Structure Methods Electronic Structure Theory > Density Functional Theory