Associate Professor Department of Physics University of Science & Technology of China
Hefei 230026, Anhui, China
zqj@ustc.edu.cn Room B-908, Material Science and Research Building
Full CV
Research Interests
Our research focuses on first-principles calculations on electronic
structure and excited carrier dynamics in different condensed matter systems.
Our goal is to understand the behavior of electrons in multiscale, including
time, energy, real and momentum space.
Employment
Mar. 2022 — now,
Associate Professor
Department of Physics
University of Science & Technology of China
Oct. 2018 — Mar. 2022,
Research Associate Professor
Department of Physics
University of Science & Technology of China
Jun. 2016 — Sep. 2018,
Postdoc
Hefei National Laboratory of Physical Sciences at the Microscale University of Science & Technology of China
Application of the non-adiabatic molecular dynamics (NAMD) approach is limited to studying carrier dynamics in the momentum space, as a supercell is required to sample the phonon excitation and electron–phonon (e–ph) interaction at different momenta in a molecular dynamics simulation. Here we develop an ab initio approach for the real-time charge carrier quantum dynamics in the momentum space (NAMD_k) by directly introducing e–ph coupling into the Hamiltonian based on the harmonic approximation. The NAMD_k approach maintains the zero-point energy and includes memory effects of carrier dynamics. The application of NAMD_k to the hot carrier dynamics in graphene reveals the phonon-specific relaxation mechanism. An energy threshold of 0.2 eV—defined by two optical phonon modes—separates the hot electron relaxation into fast and slow regions with lifetimes of pico- and nanoseconds, respectively. The NAMD_k approach provides an effective tool to understand real-time carrier dynamics in the momentum space for different materials.
@article{ZhengZ_2023_NatCompSci,
title = {\textit{Ab Initio} {Real-time Quantum Dynamics of Charge Carriers in Momentum Space}},
author+an = {1=first; 2=corresponding; 5=corresponding,highlight; 6=corresponding},
author = {Zheng, Zhenfa and Shi, Yongliang and Zhou, Jin-Jian and Prezhdo, Oleg V. and Zheng, Qijing and Zhao, Jin},
pdf = {/assets/pdf/pubs/Zhengzhenfa_NatCompSci_2023.pdf},
first_authors = {Zheng Zhenfa},
corresponding_authors = {Zhao Jin, Zheng Qijing, Shi Yongliang},
doi = {10.1038/s43588-023-00456-9},
journal = {Nature Computational Science},
publisher = {Springer Nature},
month = jun,
volume = {3},
pages = {532--541},
year = {2023}
}
Spin-orbit Coupling Induced Demagnetization in Ni: Ab Initio Nonadiabatic Molecular Dynamics Perspective
Spin-orbit coupling (SOC), which can induce spin flip during the relaxation of photoexcited charge carrier, plays a crucial role in spin dynamics. In this work, we have used time-domain ab initio nonadiabatic molecular dynamics (NAMD) method to study the SOC induced ultrafast demagnetization in Ni at
300
K
. The spin-diabatic representation using spin-polarized Kohn-Sham (KS) basis sets and spin-adiabatic representation using spinor basis sets have been applied, and both of them achieve demagnetization in Ni with a timescale around
100
fs
. The spin-diabatic representation suggests a picture that the electron-phonon coupling (EPC) provides direct energy relaxation channel among the same-spin states, while the SOC can induce spin flip. After photoexcitation, it is found the spin-minority electrons relax to the same-spin states rather than the opposite-spin states, since EPC is larger than SOC by one order of magnitude. By contrast, for the spin-majority electrons, spin flip occurs since there are no empty same-spin states as electron acceptor above the Fermi level. The different relaxation pathways for spin-majority and spin-minority electrons induce the demagnetization. The spin-adiabatic representation provides an Elliott-Yafet spin-phonon scattering picture. The SOC induced reduction of magnetic moment in Ni may induce magnon to drive further demagnetization. The ab initio NAMD simulation provides a critical angle to understand how the SOC and EPC affect demagnetization process in Ni.
Transient tuning of material properties by light usually requires intense laser fields in the nonlinear excitation regime. Here, we report ultrafast ferroelectric ordering on the surface of a paraelectric topological semimetal 1T’-MoTe2 in the linear excitation regime, with the order parameter directly proportional to the excitation intensity. The ferroelectric ordering, driven by a transient electric field created by electrons trapped ångstroms away from the surface in the image potential state (IPS), is evidenced in two-photon photoemission spectroscopy showing the energy relaxation rate proportional to IPS electron density, but with negligible change in the free-electron-like parallel dispersion. First-principles calculations reveal an improper ferroelectric ordering associated with an anharmonic interlayer shearing mode. Our findings demonstrate an ultrafast charge-based pathway for creating transient polarization orders.
@article{Dai2021,
annote = {doi: 10.1021/acs.nanolett.1c02965},
author = {Dai, Yanan and Zheng, Qijing and Ziffer, Mark E and Rhodes, Daniel and Hone, James and Zhao, Jin and Zhu, Xiaoyang},
corresponding_authors = {Zhao Jin, Zhu Xiaoyang},
first_authors = {Dai Yannan, Zheng Qijing},
doi = {10.1021/acs.nanolett.1c02965},
issn = {1530-6984},
journal = {Nano Letters},
month = nov,
number = {23},
pages = {9903--9908},
volume = {21},
publisher = {American Chemical Society},
title = {{Ultrafast Ferroelectric Ordering on the Surface of a Topological Semimetal MoTe2}},
url = {https://doi.org/10.1021/acs.nanolett.1c02965 https://pubs.acs.org/doi/10.1021/acs.nanolett.1c02965},
year = {2021},
pdf = {/assets/pdf/pubs/DynZqj_NanoLett_2021.pdf}
}
Real-Time GW-BSE Investigations on Spin-Valley Exciton Dynamics in Monolayer Transition Metal Dichalcogenide
Science Advances, 7, eabf3759 (2021) Published: Mar, 2021
We develop an ab initio nonadiabatic molecular dynamics (NAMD) method based on GW plus real-time Bethe-Salpeter equation (GW + rtBSE-NAMD) for the spin-resolved exciton dynamics. From investigations on MoS2 , we provide a comprehensive picture of spin-valley exciton dynamics where the electron-phonon (e-ph) scattering, spin-orbit interaction (SOI), and electron-hole (e-h) interactions come into play collectively. In particular, we provide a direct evidence that e-h exchange interaction plays a dominant role in the fast valley depolarization within a few picoseconds, which is in excellent agreement with experiments. Moreover, there are bright-to-dark exciton transitions induced by e-ph scattering and SOI. Our study proves that e-h many-body effects are essential to understand the spin-valley exciton dynamics in transition metal dichalcogenides and the newly developed GW + rtBSE-NAMD method provides a powerful tool for exciton dynamics in extended systems with time, space, momentum, energy, and spin resolution.
@article{JiangX2021,
corresponding_authors = {Zhao Jin},
author = {Jiang, Xiang and Zheng, Qijing and Lan, Zhenggang and Saidi, Wissam A and Ren, Xinguo and Zhao, Jin},
doi = {10.1126/sciadv.abf3759},
issn = {2375-2548},
journal = {Science Advances},
mendeley-groups = {2020_mianshang/m2},
month = mar,
number = {10},
pages = {eabf3759},
title = {{Real-Time GW-BSE Investigations on Spin-Valley Exciton Dynamics in Monolayer Transition Metal Dichalcogenide}},
url = {https://advances.sciencemag.org/lookup/doi/10.1126/sciadv.abf3759},
pdf = {/assets/pdf/pubs/JiangXiang_SciAdv_2021.pdf},
volume = {7},
year = {2021}
}
Ab Initio Nonadiabatic Molecular Dynamics Investigations on the Excited Carriers in Condensed Matter Systems
The ultrafast dynamics of photoexcited charge carriers in condensed matter systems play an important role in optoelectronics and solar energy conversion. Yet it is challenging to understand such multidimensional dynamics at the atomic scale. Combining the real-time time-dependent density functional theory with fewest-switches surface hopping scheme, we develop time-dependent ab initio nonadiabatic molecular dynamics (NAMD) code Hefei-NAMD to simulate the excited carrier dynamics in condensed matter systems. Using this method, we have investigated the interfacial charge transfer dynamics, the electron–hole recombination dynamics, and the excited spin-polarized hole dynamics in different condensed matter systems. The time-dependent dynamics of excited carriers are studied in energy, real and momentum spaces. In addition, the coupling of the excited carriers with phonons, defects and molecular adsorptions are investigated. The state-of-art NAMD studies provide unique insights to understand the ultrafast dynamics of the excited carriers in different condensed matter systems at the atomic scale. This article is categorized under: Structure and Mechanism > Computational Materials Science Molecular and Statistical Mechanics > Molecular Dynamics and Monte-Carlo Methods Electronic Structure Theory > Ab Initio Electronic Structure Methods Software > Simulation Methods.
@article{zheng2019textit,
author = {Zheng, Qijing and Chu, Weibin and Zhao, Chuanyu and Zhang, Lili and Guo, Hongli and Wang, Yanan and Jiang, Xiang and Zhao, Jin},
doi = {10.1002/wcms.1411},
issn = {17590884},
journal = {Wiley Interdisciplinary Reviews: Computational Molecular Science},
keywords = {Hefei-NAMD,excited carrier dynamics,nonadiabatic molecular dynamics,real-time time-dependent density functional theory},
number = {6},
pages = {e1411},
publisher = {Wiley Periodicals, Inc.},
corresponding_authors = {Zhao Jin},
month = mar,
title = {{Ab Initio Nonadiabatic Molecular Dynamics Investigations on the Excited Carriers in Condensed Matter Systems}},
volume = {9},
pdf = {/assets/pdf/pubs/ZhengQijing_WIRES_2018.pdf},
year = {2019}
}
Phonon-Coupled Ultrafast Interlayer Charge Oscillation at van der Waals Heterostructure Interfaces
Physical Review B, 97, 205417 (2018) Published: May, 2018
Van der Waals (vdW) heterostructures of transition-metal dichalcogenide (TMD) semiconductors are central not only for fundamental science, but also for electro- and optical-device technologies where the interfacial charge transfer is a key factor. Ultrafast interfacial charge dynamics has been intensively studied, however, the atomic scale insights into the effects of the electron-phonon (e-p) coupling are still lacking. In this paper, using time dependent ab initio nonadiabatic molecular dynamics, we study the ultrafast interfacial charge transfer dynamics of two different TMD heterostructures MoS2/WS2 and MoSe2/WSe2, which have similar band structures but different phonon frequencies. We found that MoSe2/WSe2 has softer phonon modes compared to MoS2/WS2, and thus phonon-coupled charge oscillation can be excited with sufficient phonon excitations at room temperature. In contrast, for MoS2/WS2, phonon-coupled interlayer charge oscillations are not easily excitable. Our study provides an atomic level understanding on how the phonon excitation and e-p coupling affect the interlayer charge transfer dynamics, which is valuable for both the fundamental understanding of ultrafast dynamics at vdW hetero-interfaces and the design of novel quasi-two-dimensional devices for optoelectronic and photovoltaic applications.
@article{zheng2018phonon,
author = {Zheng, Qijing and Xie, Yu and Lan, Zhenggang and Prezhdo, Oleg V. and Saidi, Wissam A. and Zhao, Jin},
doi = {10.1103/PhysRevB.97.205417},
isbn = {2469-9950
2469-9969},
issn = {24699969},
journal = {Physical Review B},
month = may,
number = {20},
pages = {205417},
publisher = {American Physical Society},
title = {{Phonon-Coupled Ultrafast Interlayer Charge Oscillation at van der Waals Heterostructure Interfaces}},
corresponding_authors = {Zhao Jin},
pdf = {/assets/pdf/pubs/ZhengQijing_PRB_2018.pdf},
url = {https://link.aps.org/doi/10.1103/PhysRevB.97.205417},
volume = {97},
year = {2018}
}
Delocalized Impurity Phonon Induced Electron-Hole Recombination in Doped Semiconductors
Nano Letters, 18, 1592–1599 (2018) Published: Mar, 2018
Semiconductor doping is often proposed as an effective route to improving the solar energy conversion efficiency by engineering the band gap; however, it may also introduce electron-hole (e-h) recombination centers, where the determining element for e-h recombination is still unclear. Taking doped TiO2 as a prototype system and by using time domain ab initio nonadiabatic molecular dynamics, we find that the localization of impurity-phonon modes (IPMs) is the key parameter to determine the e-h recombination time scale. Noncompensated charge doping introduces delocalized impurity-phonon modes that induce ultrafast e-h recombination within several picoseconds. However, the recombination can be largely suppressed using charge-compensated light-mass dopants due to the localization of their IPMs. For different doping systems, the e-h recombination time is shown to depend exponentially on the IPM localization. We propose that the observation that delocalized IPMs can induce fast e-h recombination is broadly applicable and can be used in the design and synthesis of functional semiconductors with optimal dopant control.
@article{zhang2018delocalized,
author = {Zhang, Lili and Zheng, Qijing and Xie, Yu and Lan, Zhenggang and Prezhdo, Oleg V. and Saidi, Wissam A. and Zhao, Jin},
doi = {10.1021/acs.nanolett.7b03933},
issn = {15306992},
journal = {Nano Letters},
keywords = {Semiconductor doping,electron-hole recombination,impurity-phonon mode,nonadiabaic molecular dynamics},
month = mar,
number = {3},
pages = {1592--1599},
pmid = {29393653},
publisher = {American Chemical Society},
title = {{Delocalized Impurity Phonon Induced Electron-Hole Recombination in Doped Semiconductors}},
pdf = {/assets/pdf/pubs/ZhangLili_NanoLett_2018.pdf},
corresponding_authors = {Zhao Jin},
first_authors = {Zheng Qijing},
url = {http://pubs.acs.org/doi/10.1021/acs.nanolett.7b03933},
volume = {18},
year = {2018}
}
Phonon-Assisted Ultrafast Charge Transfer at van der Waals Heterostructure Interface
The van der Waals (vdW) interfaces of two-dimensional (2D) semiconductor are central to new device concepts and emerging technologies in light-electricity transduction where the efficient charge separation is a key factor. Contrary to general expectation, efficient electron-hole separation can occur in vertically stacked transition-metal dichalcogenide heterostructure bilayers through ultrafast charge transfer between the neighboring layers despite their weak vdW bonding. In this report, we show by ab initio nonadiabatic molecular dynamics calculations, that instead of direct tunneling, the ultrafast interlayer hole transfer is strongly promoted by an adiabatic mechanism through phonon excitation occurring on 20 fs, which is in good agreement with the experiment. The atomic level picture of the phonon-assisted ultrafast mechanism revealed in our study is valuable both for the fundamental understanding of ultrafast charge carrier dynamics at vdW heterointerfaces as well as for the design of novel quasi-2D devices for optoelectronic and photovoltaic applications.
@article{zheng2017phonon,
annote = {From Duplicate 1 (Phonon-Assisted Ultrafast Charge Transfer at van der Waals Heterostructure Interface - Zheng, Qijing; Saidi, Wissam A.; Xie, Yu; Lan, Zhenggang; Prezhdo, Oleg V.; Petek, Hrvoje; Zhao, Jin)
Petek, Hrvoje/A-3912-2009; Lan, Zhenggang/H-3676-2012; xie, yu/; Saidi, Wissam A./
Petek, Hrvoje/0000-0001-9605-2590; xie, yu/0000-0001-8925-6958; Saidi, Wissam A./0000-0001-6714-4832
1530-6992},
author = {Zheng, Qijing and Saidi, Wissam A. and Xie, Yu and Lan, Zhenggang and Prezhdo, Oleg V. and Petek, Hrvoje and Zhao, Jin},
corresponding_authors = {Zhao Jin},
doi = {10.1021/acs.nanolett.7b03429},
issn = {15306992},
journal = {Nano Letters},
keywords = {nonadiabatic molecular dynamics,ultrafast charge transfer,van der Waals heterointerface},
month = oct,
number = {10},
pages = {6435--6442},
pmid = {28914539},
publisher = {American Chemical Society},
title = {{Phonon-Assisted Ultrafast Charge Transfer at van der Waals Heterostructure Interface}},
pdf = {/assets/pdf/pubs/ZhengQijing_NanoLett_2017.pdf},
url = {https://pubs.acs.org/doi/10.1021/acs.nanolett.7b03429},
volume = {17},
year = {2017}
}
Ultrafast Dynamics of Photongenerated Holes at a CH3OH/TiO2 Rutile Interface
Journal of the American Chemical Society, 138, 13740–13749 (2016) Published: Oct, 2016
Photogenerated charge carrier dynamics near molecule/TiO2 interfaces are important for the photocatalytic and photovoltaic processes. To understand this fundamental aspect, we performed a time-domain ab initio nonadiabatic molecular dynamics study of the photogenerated hole dynamics at the CH3OH/rutile TiO2(110) interface. We studied the forward and reverse hole transfer between TiO2 and CH3OH as well as the hole energy relaxation to the valence band maximum. First, we show that the hole-trapping ability of CH3OH depends strongly on the adsorption structure. Only when the CH3OH is deprotonated to form chemisorbed CH3O will ∼15% of the hole be trapped by the molecule. Second, we find that strong fluctuations of the HOMO energies of the adsorbed molecules induced by electron-phonon coupling provide additional channels, which accelerate the hole energy relaxation. Third, we demonstrate that the charge transfer and energy relaxation processes depend significantly on temperature. When the temperature decreases from 100 to 30 K, the forward hole transfer and energy relaxation processes are strongly suppressed because of the reduction of phonon occupation. These results indicate that the molecule/TiO2 energy level alignment, thermal excitation of a phonon, and electron-phonon coupling are the key factors that determine the photogenerated hole dynamics. Our studies provide valuable insights into the photogenerated charge and energy transfer dynamics at molecule/semiconductor interfaces.
@article{chu2016ultrafast,
author = {Chu, Weibin and Saidi, Wissam A. and Zheng, Qijing and Xie, Yu and Lan, Zhenggang and Prezhdo, Oleg V. and Petek, Hrvoje and Zhao, Jin},
doi = {10.1021/jacs.6b08725},
isbn = {1520-5126 (Electronic)
0002-7863 (Linking)},
issn = {15205126},
journal = {Journal of the American Chemical Society},
month = oct,
number = {41},
pages = {13740--13749},
pmid = {27656768},
publisher = {American Chemical Society},
title = {{Ultrafast Dynamics of Photongenerated Holes at a CH3OH/TiO2 Rutile Interface}},
corresponding_authors = {Zheng Qijing, Zhao Jin},
url = {https://pubs.acs.org/doi/10.1021/jacs.6b08725},
pdf = {/assets/pdf/pubs/ChuWeibin_JACS_2016.pdf},
volume = {138},
year = {2016}
}
