Two-dimensional (2D) heterostructures composed of transition-metal dichalcogenide atomic layers are the new frontier for novel optoelectronic and photovoltaic device applications. Some key properties that make these materials appealing, yet are not well understood, are ultrafast hole/electron dynamics, interlayer energy transfer and the formation of interlayer hot excitons. Here, we study photoexcited electron/hole dynamics in a representative heterostructure, the MoS/WSe interface, which exhibits type II band alignment. Employing time-dependent density functional theory in the time domain, we observe ultrafast charge dynamics with lifetimes of tens to hundreds of femtoseconds. Most importantly, we report the discovery of an interfacial pathway in 2D heterostructures for the relaxation of photoexcited hot electrons through interlayer hopping, which is significantly faster than intralayer relaxation. This finding is of particular importance for understanding many experimentally observed photoinduced processes, including charge and energy transfer at an ultrafast time scale (<1 ps).

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Optical control of structural and electronic properties of Weyl semimetals allows development of switchable and dissipationless topological devices at the ultrafast scale. An unexpected orbital-selective photoexcitation in type-II Weyl material WTe2 is reported under linearly polarized light (LPL), inducing striking transitions among several topologically-distinct phases mediated by effective electron-phonon couplings. The symmetry features of atomic orbitals comprising the Weyl bands result in asymmetric electronic transitions near the Weyl points, and in turn a switchable interlayer shear motion with respect to linear light polarization, when a near-infrared laser pulse is applied. Consequently, not only annihilation of Weyl quasiparticle pairs, but also increasing separation of Weyl points can be achieved, complementing existing experimental observations. In this work, we provide a new perspective on manipulating the Weyl node singularity and coherent control of electron and lattice quantum dynamics simultaneously.

The past decades have witnessed the success of ground‐state density functional theory capturing static electronic properties of various materials. However, for time dependent processes especially those involving excited states, real‐time time‐dependent density functional theory (rt‐TDDFT) and advanced nonadiabatic algorithms are essential, especially for practical simulations of molecules and materials under the occurrence of ultrafast laser field. Here we summarize the recent progresses in developing rt‐TDDFT approaches within numerical atomic orbitals and planewave formalisms, as well as the efforts combining rt‐TDDFT and ring polymer molecular dynamics to take into account nuclear quantum effects in quantum electronic‐nuclear dynamic simulations. Typical applications of first‐principles dynamics of excited electronic states including high harmonic generation, charge density wave, photocatalytic water splitting, as well as quantum nuclear motions in ozone and graphene, are presented to demonstrate the features and advantages of these methods. The progresses in method developments and practical applications provide unprecedented insights into nonadiabatic dynamics of excited states in the Ehrenfest scheme and beyond, towards a comprehensive understanding of excited electronic structure, electron–phonon interactions, photoinduced charge transfer and chemical reactions, as well as quantum nuclear motions in excited states. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods Electronic Structure Theory > Density Functional Theory Molecular and Statistical Mechanics > Molecular Dynamics and Monte‐Carlo Methods

To elucidate the nature of light-driven photocatalytic water splitting, a polymeric semiconductorgraphitic carbon nitride (g-C3N4)has been chosen as a prototype substrate for studying atomistic water spitting processes in realistic environments. Our nonadiabatic quantum dynamics simulations based on real-time time-dependent density functional theory reveal explicitly the transport channel of photogenerated charge carriers at the g-C3N4/water interface, which shows a strong correlation to bond re-forming. A three-step photoreaction mechanism is proposed, whereas the key roles of hole-driven hydrogen transfer and interfacial water configurations were identified. Immediately following photocatalytic water splitting, atomic pathways for the two dissociated hydrogen atoms approaching each other and forming the H2 gas molecule are demonstrated, while the remanent OH radicals may form intermediate products (e.g., H2O2). These results provide critical new insights for the characterization and further development of efficient water-splitting photocatalysts from a dynamic perspective.

Exact or numerical solution of the time dependent Schrödinger equation (TDSE) in the presence of external field is a major challenge for modern computer simulations of materials. However, many nonadiabatic phenomena such as chemical reactions [1-3], electron-phonon couplings [4,5] and ultrafast dynamics [6-8] require a quantum treatment of many-body TDSE in practical simulations. Some ab initio quantum dynamic simulations have been carried out in the past [9][10][11][12][13][14][15][16][17][18]. Full quantum dynamics such as multi-configuration time-dependent Hartree [9, 10] (MCTDH) can provide exact results for small molecules, but MCTDH is restricted by the number of nuclear degrees of freedom that can be explicitly accounted for in the method, preventing its efficient use for large molecules and complex materials. An advanced method, variational multiconfigurational Gaussian wave packet method [18], offers a way to solve on-the-fly the time-dependent molecular Schrödinger equation, including all quantum nuclear effects, and has been coupled with ab initio electronic structure methods. Another popular approach, multiple spawning [11], can converge to exact solutions for small systems but is limited by the truncation of large basis set. Involving classical nuclear approximations, fewest-switches surface-hopping algorithm [12,13] (FSSH) and Ehrenfest dynamics [14][15][16][17] are the dominating simple approaches feasible for large-scale mixed quantum-classical dynamics simulations of realistic materials at the present.To treat the quantum property of nuclei, ring polymer molecular dynamics (RPMD) based on imaginarytime path integral simulations of nuclear trajectory has been introduced [19,20]. Recently, Tully et al has made a breakthrough developing the nonadiabatic dynamics simulation method of RPMD implemented with FSSH, to incorporate proper treatment of quantum nuclear behaviors in nonadiabatic surface hopping simulations

The last few decades have witnessed the extraordinary advances in theoretical and experimental tools, which have enabled the manipulation and monitoring of ultrafast dynamics with high precisions. For modeling dynamical responses beyond the perturbative regime, computational methods based on time-dependent density functional theory (TDDFT) are the optimal choices. Here, we introduce TDAP (time-dependent ab initio propagation), a first-principle approach that is aimed at providing robust dynamic simulations of light-induced, highly nonlinear phenomena by real-time calculation of combined photonic, electronic, and ionic quantum mechanical effects within a TDDFT framework. We review the implementation of real-time TDDFT with numerical atomic orbital formalisms, which has enabled high-accuracy, large-scale simulations with moderate computational cost. The newly added features, i.e., the time-dependent electric field gauges and controllable ionic motion make the method especially suitable for investigating ultrafast electron-nuclear dynamics in complex periodic and semiperiodic systems. An overview of the capabilities of this first-principle method is provided by showcasing several representative applications including high-harmonic generation, tunable phase transitions, and new emergent states of matter. The method demonstrates a great potential in obtaining a predictive and comprehensive understanding of quantum dynamics and interactions in a wide range of materials at the atomic and attosecond space-time scale.

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