Real-time time dependent density functional theory with numerical atomic orbital basis set: methodology and applications

Real-time time dependent density functional theory (rt-TDDFT) approach directly provides the time domain evolution of electronic wave functions together with ionic movements, presenting a versatile way of real time tracking ultrafast dynamics and phenomena either in perturbative regime or in non-perturbative regime. Thus, rt-TDDFT is a unique ab initio quantum method applicable for the exploration of strong field physics that is beyond the linear response theory. Numerical implementations of the rt-TDDFT based on planewaves and real-space grids have been demonstrated in recent years. However, the above two methods are suitable for the efficient treatment of low energy excitation on the scale of a few electron volts in a small size system. In this paper, we present a state-of-the-art real-time TDDFT approach as implemented in the time dependent ab initio package (TDAP). By employing atomic orbital basis sets, which are small in size and fast in performance, we are able to simulate a large-size system for long electronic propagation time with less computational cost while maintaining relatively high accuracy. The length and velocity-gauge of electromagnetic field are both implemented, showing the flexibility and credibility in applying our methods to various laser induced phenomena in diverse systems including solids, interfaces and two-dimensional materials. Furthermore, recently developed k-resolved algorithm ensures the possibility of handling the problems with a unit cell approach, which significantly reduces the formidable computational costs of traditional rt-TDDFT simulations. Detailed flow and implementation of this method are discussed in this paper, and several quintessential examples for applications are introduced. First, we use the present method to calculate the photoabsorption properties of armchair graphene nanoribbons and monitor the excitation details with momentum resolution. Then, we simulate laser melting of silicon, which captures the most important features of nonthermal melting observed in experiment, and further reveals that it can be attributed to drastic laser-induced change in bonding electron density and subsequent decrease in the melting barrier. After that, a model MoS2/WS2 bilayer system is used as an example to show how our method can be used to monitor the electronic dynamics in such a van der Waals heterostructure. Finally, we show the possibility of controlling the electron dynamic process to enhance high harmonic generation intensity and generate isolated attosecond pulse in monolayer MoS2 via two-color field. Most of the above examples present new ideas in their respective areas and demonstrate that our method has a great potential application in studying interesting ultrafast dynamics phenomena in a wide range of quantum systems.