Nonadiabatic molecular dynamics with decoherence and detailed balance under a density matrix ensemble formalism

2020

J. Phys. Chem. A

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Real time time dependent density functional theory (rt-TDDFT) has now been used to study a wide range of problems, from optical excitation, to charge transfer, to ion collision, to ultrafast phase transition. However, conventional rt-TDDFT Ehrenfest dynamics for nuclear movement lacks a few critical features to describe many problems: the detail balance between state transition, decoherence for the wave function evolution, and stochastic branching of the nuclear trajectory. There are many-body formalisms to describe such nonadiabatic molecular dynamics, especially the ones based on mixed quantum/classical simulations, like the surface hopping and wave function collapsing schemes. However, there are still challenges to implement such many-body formalisms to the rt-TDDFT simulations, especially for large systems where the excited state electronic structure configuration space is large. Here we introduce two new algorithm for nonadiabatic rt-TDDFT simulations: the first is a Boltzmann factor algorithm which introduces decoherence and detailed balance in the carrier dynamics, but uses mean field theory for nuclear trajectory. The second is a natural orbital branching (NOB) formalism, which use time dependent density matrix for electron evolution, and natural orbital to collapse the wave function upon. It provides decoherence, detailed balance and trajectory branching properties. We have tested these methods for a molecule radiolysis decay problem. We found these methods can be used to study such radiolysis problem in which the molecule is broken into many fragments following complex electronic structure transition paths. The computational time of NOB is similar to the original plain rt-TDDFT simulations File list (2) download file view on ChemRxiv manuscript_NOB.pdf (1.61 MiB) download file view on ChemRxiv Supplementary_Material.pdf (151.04 KiB) A natural orbital branching scheme for time dependent density functional theory nonadiabatic simulations

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Natural Orbital Branching Scheme for Time-Dependent Density Functional Theory Nonadiabatic Simulations

2020

J. Phys. Chem. A

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“…Our NAMD is based on a newly developed algorithm called P-matrix formalism. 50,51 Unlike previous NAMD methods where multi-trajectory stochastic simulations are used to represent the ensemble of the trajectories to include the detailed balance and decoherence effect, [40][41][42][44][45][46] in our P-matrix formalism, a single run can represent a whole ensemble result while including the detailed balance and decoherence effect. In this formalism, the decoherence can be introduced naturally, and detailed balance is also satisfied.…”

mentioning

confidence: 99%

“…Different from other NAMD methods, the time-dependent Schrodinger's equation is reformulated following the P-matrix equation in a density matrix formalism. 50 In this way, it is possible to take into account the detailed balance and decoherence effect at the same time. The detailed balance is important in order to describe the cooling process, while the decoherence (dephasing) also influences the cooling rate.…”

mentioning

confidence: 99%

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Ultrafast Hot Carrier Injection in Au/GaN: The Role of Band Bending and the Interface Band Structure

Zheng

2019

J. Phys. Chem. Lett.

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Plasmon photochemistry can potentially play a significant role in photocatalysis. To realize this potential, it is critical to enhance the plasmon excited hot carrier transfer and collection. However, the lack of atomistic understanding of the carrier transfer across the interface, especially when the carrier is still "hot", makes it challenging to design more efficient system. In this work, we apply the non-adiabatic molecular dynamics simulation to study hot carrier dynamics in the system of Au nanocluster on top of GaN surface. By setting up the initial excited hole in Au, the carrier transfer from Au to GaN is found to be on a sub-pico second time scale. The hot hole first cools to the band edge of Au d-states while it transfers to GaN. After the hole has cooled down to the band edge of GaN, we find some of the charges can return back to Au. By applying different external potentials to mimic the Schottky-barrier band bending, the returning charge can be reduced, demonstrating the importance of the internal electric field. Finally, with the understanding of the carrier transfer's pathway, we suggest 1 that a ZnO layer between GaN and Au can effectively block the "cold" carrier from 16 returning back to Au but still allow the hot carrier to transfer from Au to GaN.

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

Liu

Chen

et al. 2021

WIREs Comput Mol Sci

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.