Browsing by Author "Yu, Le"

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Benchmark Performance of Global Switching versus Local Switching for Trajectory Surface Hopping Molecular Dynamics Simulation: Cis <-> Trans Azobenzene Photoisomerization
(2017-05-19)
Yue, Ling
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Yu, Le
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Xu, Chao
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Lei, Yibo
;
Liu, Yajun
A newly developed global switching algorithm that does not require calculation of nonadiabatic coupling vectors reduces computational costs significantly. However, the accuracy of this simplest nonadiabatic molecular dynamic method has not been extensively compared with the conventional Tully's fewest switches. It is necessary to demonstrate the accuracy of this global switching algorithm. An extensive comparison between local and global switching on-the-fly trajectory surface hopping molecular dynamics is performed for cis-to-trans (800 sampling trajectories) and trans-to-cis (600 sampling trajectories) azobenzene photoisomerization at the OM2/MRCI level. The global switching algorithm is coded into the Newton-X program package. Excellent agreement between the two switching algorithms is obtained not only for highly averaged quantities of quantum yields and lifetimes, but also for detailed contour patterns of product distributions, hopping spot distributions and hopping directions in terms of conical intersections between ground and the first excited states. Therefore, the global switching trajectory surface hopping method can be applied to larger complex systems in which nonadiabatic coupling is not available for excited-state molecular dynamic simulations.
Chiral conversion and periodical decay in bridged-azobenzene photoisomerization: an ab initio on-the-fly nonadiabatic dynamics simulation
(2016-01-01)
Gao, Wanqing
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Yu, Le
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Zheng, Xiaolei
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Lei, Yibo
;
Zhu, Chaoyuan
With the implementation of global nonadiabatic switching probability algorithm based on the Zhu-Nakamura theory, we performed on-the-fly trajectory surface hopping simulations at the CASSCF level to analyze the cis <-> trans photoisomerization mechanism of bridged-azobenzene upon S-1 excitation. The cis-to-trans isomerization process was initiated by the pedal-like twist of -N=N- moiety and observed hopping to S-0 mainly via the cis-form conical intersection region. While, the trans-to-cis process is induced by the nonsymmetrical torsion motion toward the central eight-membered ring and encountered surface hopping through another conical region lying in the middle of the isomerization pathway. In cis-to-trans photoisomerization, we also observed a particular chiral conversion pathway with surface hopping occurs at CI-trans conical region. The trajectories followed this pathway possess relative longer excited state lifetimes as the similar to 40 fs initial stage oscillation in the cis Franck-Condon region. Moreover, the periodical population decay pattern of S-1 state in trans-to-cis process was observed with an interval of similar to 16 fs.
Excited-state E -> Z photoisomerization mechanism unveiled by ab initio nonadiabatic molecular dynamics simulation for hemithioindigo-hemistilbene
(2017-05-21)
Yang, Meihong
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Huo, Chunyan
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Li, Anyang
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Lei, Yibo
;
Yu, Le
The Zhu-Nakamura formulas based on on-the-fly trajectory surface hopping dynamics simulations at the two-state-averaged CASSCF level were employed to investigate the E -> Z photoisomerization mechanisms of hemithioindigo-hemistilbene (HTI) upon S-1 excitation. Seven conical intersections were observed along the isomerization pathways, which were composed of double bond torsion, benzene ring torsion, inversion and pyramidalization motions, and only three of them were found to play a role in the dynamics simulations started at S-1 E-HTI. The dominant isomerization pathway proceeds via central double bond torsion together with pyramidal and tilt motions to some extent (hop via CI5) and accounts for all the reactive trajectories. On the other hand, the two pathways that involve the conical zones lie in the vicinity of the E-form Franck-Condon region (CI7) and proceed along the combined central double bond and benzene ring torsion route (CI3/CI4) with generation of the E products. Within the 332 simulated trajectories, 66 hop to the ground state and only 19 switch to the Z product. The estimated quantum yield of 0.057 (19 in 332) agrees well with the reported experimental value of 0.053 +/- 0.016. The excited-state lifetimes span a wide region from hundreds of femtoseconds to several picoseconds, depending on the time for vibrational relaxation and number of cycles for periodical mixed mode torsion.
Intersystem crossing-branched excited-state intramolecular proton transfer for o-nitrophenol: An ab initio on-the-fly nonadiabatic molecular dynamic simulation
(2016-05-25)
Xu, Chao
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Yu, Le
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Zhu, Chaoyuan
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Yu, Jianguo
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Cao, Zexing
The 6SA-CASSCF(10, 10)/6-31G (d, p) quantum chemistry method has been applied to perform on-the-fly trajectory surface hopping simulation with global switching algorithm and to explore excited-state intramolecular proton transfer reactions for the o-nitrophenol molecule within low-lying electronic singlet states (S-0 and S-1) and triplet states (T-1 and T-2). The decisive photoisomerization mechanisms of o-nitrophenol upon S-1 excitation are found by three intersystem crossings and one conical intersection between two triplet states, in which T-1 state plays an essential role. The present simulation shows branch ratios and timescales of three key processes via T-1 state, non-hydrogen transfer with ratio 48% and timescale 300 fs, the tunneling hydrogen transfer with ratios 36% and timescale 10 ps, and the direct hydrogen transfer with ratios 13% and timescale 40 fs. The present simulated timescales might be close to low limit of the recent experiment results.
Landscapes of Four-Enantiomer Conical Intersections for Photoisomerization of Stilbene: CASSCF Calculation
(2014-10-02)
Lei, Yibo
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Yu, Le
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Zhou, Bo
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Zhu, Chaoyuan
;
Wen, Zhenyi
The photoisomerization of cis- and trans-stilbene through conical intersections (CI) is mainly governed by four dihedral angles around central C=C double bonds. The two of them are C-C=C-C and H-C=C-H dihedral angles that are found to form a mirror rotation coordinate, and the mirror plane appears at the two dihedral angles equal to zeros with which the middle state is defined through partial optimization. There exist the first-type of hula-twist-CI enantiomers, the second-type of hula-twist-CI enantiomers, the first-type of one-bond-flip-CI enantiomers, and the second type of one-bond-flip-CI enantiomers as well as cis-enantiomers and trans-enantiomers with respect to this mirror plane. The complete active space self-consistent field method is employed to calculate minimum potential energy profile along the mirror rotation coordinate for each enantiomers, and it is found that the left-hand manifold and the right-hand manifold of potential energy surfaces can be energetically transferred via photoisomerization. Furthermore, two-dimensional potential energy surfaces in terms of the branching plane g-h coordinates are constructed at vicinity of each conical intersection, and the landscapes of conical intersections show distinct feature, and in excited-state four potential wells separated in different section of g-h plane related to different conical intersections which indicate different photoisomerization pathways.
Methyl substitution enhanced photoisomerization of trans,trans-1,4-diphenyl-1,3-butadiene: direct ab initio trajectory surface hopping dynamic simulations
(2018-01-28)
Fan, Yueqian
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Chen, Juan
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Yu, Le
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Li, Anyang
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Zhai, Gaohong
Single methyl group substitution on the p-position of the phenyl ring (tt-DPB-me1) or the conjugated CQC bond (tt-DPB-me2) has been found to enhance the photoisomerization efficiency for two trans, trans-1,4-diphenyl-1,3-butadiene (tt-DPB) derivatives by performing direct ab initio trajectory surface hopping dynamics simulations. With implementation of the Zhu-Nakamura global switching algorithm, on-the-fly trajectory surface hopping dynamics simulations based on the ground state and first excited state potential energies and their gradients calculated by the two state averaged complete active space self-consistent field method with basis set 6-31G were propagated up to 3000 femtoseconds. Four-hundred sampling trajectories have been performed for both tt-DPB-me1 and tt-DPB-me2, and five distinctive photoisomerization pathways were observed for both of them. Among which, One Bond Flipping (OBF) and Hula-Twist (HT) are the dominant photoisomerization mechanisms. The lifetime of the S1 state is estimated to be 1423.0 fs (819.0 fs), and the photoisomerization quantum yields are 0.088 (0.378) in tt -> ct , 0.070 (0.015) in tt -> ct and 0.073 (0.065) in tt -> cc for tt-DPB-me1 (tt-DPB-me2). By analyzing the dynamics simulation data, it can be concluded that closer methyl substitution with respect to the central C=C double bond results in a higher percentage of the corresponding photoisomerization products. The present simulation results are in agreement with the ultrafast spectroscopy measurements, which unveil the photoisomerization mechanisms of tt-DPB derivatives and present useful physical insights on how to tune the photoisomerization of the substituted DPB.
Photoisomerization mechanisms from trans, trans-1,4-diphenyl-1,3-butadiene: CASSCF on-the-fly trajectory surface hopping dynamic simulations
(2016-04-07)
Zheng, Xiaolei
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Zhai, Gaohong
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Gao, Wanqing
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Lei, Yibo
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Yu, Le
We have employed the SA2-CAS(4,4)/6-31G ab initio method together with an on-the-fly global-switching trajectory surface hopping algorithm to simulate photoisomerization reaction dynamics from reactant trans, trans-1,4-diphenyl-1,3-butadiene (DPB) to products cis,trans-DPB and cis,cis-DPB. This topic has been extensively studied experimentally and the present theoretical study is the first to simulate DPB photoisomerization reaction dynamics as far as we know. With total 600 sampling trajectories, 300 actively contribute to isomerization reaction via two conical intersections between the electronic ground and the first excited states. Simulated quantum yields of photoisomerization to cis, trans-DPB and cis, cis-DPB are 0.09 and 0.045, which are in good agreement with the experimental values of 0.07-0.25 and 0.02, respectively. The lifetime of the first excited state is estimated as 702 fs. The present simulation has shown two reactive photoisomerization mechanisms, namely one bond twist (OBT) and bicycle pedal (BP), and two non-reactive photoisomerization mechanisms, namely single bond torsion (SBT) and reverse torsion (RT) with respect to the central backbone CC bonds. We believe that the present theoretical work can benefit the experiments on photoisomerization of DPB derivates.
Photoisomerization Reaction Mechanisms of o-Nitrophenol Revealed by Analyzing Intersystem Crossing Network at the MRCI Level
(2015-10-22)
Xu, Chao
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Yu, Le
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Zhu, Chaoyuan
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Yu, Jianguo
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應用化學系分子科學碩博班
6SA-CASSCF(10, 10) /6-31G (d, p) and MRCl/cc-pVDZ methods were performed to probe photoisomerization reaction mechanisms of o-nitrophenol. Two low-lying singlet electronic states (S-0 and S-1) and two low-lying triplet electronic states (T-1 and T-2) were found to weave an intersystem crossing network in which a dominant stepwise photoisomerization provides a very efficient reaction pathway; the reaction takes place in the wide region of crossing seam-surface woven by S-1 and T-1 states first, followed by T-1 and S-0 states. Both intersystem crossing regions show strong spin orbital coupling in the order of 40 wavenumbers. All nitro and aci-nitro isomers and transition states on four electronic potential energy surfaces are calculated along with analysis of both dominant and subdominant relaxation pathways, especially weak spin-orbital coupling (similar to 10 wavenumbers) between T-2 and S-1 states and effective conical intersection between T-2 and T-1 states opening a new relaxation pathway S-1 -> T-2 -> T-1.
Photorelaxation Pathways of 4-(N,N-Dimethylamino)-4 '-nitrostilbene Upon S-1 Excitation Revealed by Conical Intersection and Intersystem Crossing Networks
(2020-05-01)
He, Ziyue
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Xue, Ruidi
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Lei, Yibo
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Yu, Le
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Zhu, Chaoyuan
Multi-state n-electron valence state second order perturbation theory (MS-NEVPT2) was utilized to reveal the photorelaxation pathways of 4-(N,N-dimethylamino)-4 '-nitrostilbene (DANS) upon S-1 excitation. Within the interwoven networks of five S-1/S-0 and three T-2/T-1 conical intersections (CIs), and three S-1/T-2, one S-1/T-1 and one S-0/T-1 intersystem crossings (ISCs), those competing nonadiabatic decay pathways play different roles in trans-to-cis and cis-to-trans processes, respectively. After being excited to the Franck-Condon (FC) region of the S-1 state, trans-S-1-FC firstly encounters an ultrafast conversion to quinoid form. Subsequently, the relaxation mainly proceeds along the triplet pathway, trans-S-1-FC -> ISC-S-1/T-2-trans -> CI-T-2/T-1-trans -> ISC-S-0/T-1-twist -> trans- or cis-S-0. The singlet relaxation pathway mediated by CI-S-1/S-0-twist-c is hindered by the prominent energy barrier on S-1 surface and by the reason that CI-S-1/S-0-trans and CI-S-1/S-0-twist-t are both not energetically accessible upon S-1 excitation. On the other hand, the cis-S-1-FC lies at the top of steeply decreasing potential energy surfaces (PESs) towards the CI-S-1/S-0-twist-c and CI-S-1/S-0-DHP regions; therefore, the initial twisting directions of DN and DAP moieties determine the branching ratio between alpha(C=C) twisting (cis-S-1-FC -> CI-S-1/S-0-twist-c -> trans- or cis-S-0) and DHP formation relaxation pathways (cis-S-1-FC -> CI-S-1/S-0-DHP -> DHP-S-0) on the S-1 surface. Moreover, the DHP formation could also take place via the triplet relaxation pathway, cis-S-1-FC -> ISC-S-1/T-1-cis -> DHP-T-1 -> DHP-S-0, however, which may be hindered by insufficient spin-orbit coupling (SOC) strength. The other triplet pathways for cis-S-1-FC mediated by ISC-S-1/T-2-cis are negligible due to the energy or geometry incompatibility of possible consecutive stepwise S-1 -> T-2 -> T-1 or S-1 -> T-2 -> S-1 processes. The present study reveals photoisomerization dynamic pathways via conical intersection and intersystem crossing networks and provides nice physical insight into experimental investigation of DANS.
Probing the pi -> pi* photoisomerization mechanism of cis-azobenzene by multi-state ab initio on-the-fly trajectory dynamics simulation
(2015-01-01)
Yu, Le
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Xu, Chao
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Zhu, Chaoyuan
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應用化學系分子科學碩博班
;
Institute of Molecular science
Based on a newly developed algorithm to compute global nonadiabatic switching probability by using only electronic adiabatic potential energy surfaces and gradients, we performed on-the-fly, trajectory-surface hopping simulations at the 5SA-CASSCF(6,6)/6-31G quantum level to probe the pi -> pi* photoisomerization mechanism of the azobenzene within four singlet low-lying electronic states (S-0, S-1, S-2, and S-3) coupled with a complicated conical intersection network. We found that four conical intersections between the S-1 and S-2 states (one is near the cis-isomer region, another near the trans-isomer region, and two others between cis and trans) play the most important roles for understanding the photoisomerization mechanism of azobenzene upon S-2 and S-3 pi pi* excitation. We studied six cases to demonstrate the photoisomerization mechanism in detail by choosing eight (six) typical reactive (nonreactive) trajectories, namely, two-step fast-fast processes having lifetimes of several tenths to one hundred femtoseconds and two-step, fast-slow and slow-slow processes having lifetimes of several hundred to one thousand femtoseconds. We found for the first time from simulation that once a trajectory visits the conical intersection near the trans-isomer after pi pi* excitation, it could rapidly go through the inversion pathway to trans-azobenzene, and confirms the most recent experimental observations. We performed 536 sampling trajectories (336 from S-2 and 200 from S-3), initially starting from the Franck-Condon region of cis-azobenzene, and obtained a total reactive quantum yield of 0.3-0.45 in very good agreement with recent experimental results of 0.24-0.50. Moreover, the current method can estimate overall nonadiabatic transition probability for each sampling trajectory from beginning to end. This can greatly accelerate convergence of nonadiabatic molecular dynamic simulation, and, for instance, results in a quantum yield of 0.53 estimated from only eight typical reactive trajectories.
Probing the pi -> pi* photoisomerization mechanism of trans-azobenzene by multi-state ab initio on-the-fly trajectory dynamics simulations
(2018-10-07)
Xu, Chao
;
Yu, Le
;
Gu, Feng Long
;
Zhu, Chaoyuan
;
交大名義發表
Global nonadiabatic switching on-the-fly trajectory surface hopping simulations at the 5SA-CASSCF(6,6)/6-31G quantum level have been employed to probe the photoisomerization mechanism of trans-azobenzene upon pi pi* excitation within four coupled singlet low-lying electronic states (S-0, S-1, S-2, and S-3). We have performed 586 sampling trajectories (331 starting from S-2 and 255 from S-3), and we found about half of the sampling trajectories staying on S-1 or S-2 states as resonances and the other half of them ending on the ground S-0 state as active trajectories. The present simulation has demonstrated that there are six distinct photoisomerization pathways which can be summarized as three categories; one is the newly opened inversion-inversion nonreactive isomerization pathway accounting for 40% (34%) of active trajectories at a time constant of 80 fs (320 fs), the other is the inversion-torsion reactive and nonreactive isomerization pathways accounting for 40% (20%) of active trajectories at a time constant of 880 fs (1700 fs), and the third is the torsion-torsion reactive and nonreactive isomerization pathways accounting for 20% (46%) of active trajectories at a time constant of 780 fs (1000 fs) upon S-2 (S-3) pi pi* excitation. The simulated total reactive quantum yield for trans-azobenzene photoisomerization upon S-2 (S-3) pi pi* excitation is about 0.11 (0.13) which is in good agreement with recent experimental results of 0.09-0.20. Furthermore, the newly opened inversion-inversion nonreactive isomerization pathway from the present simulation agrees well with cascade experimental measurements of the S-n -> S-1 -> S-0 relaxation mechanism in both branching ratio and time constant.
Quantum yields of singlet and triplet chemiexcitation of dimethyl 1,2-dioxetane: ab initio nonadiabatic molecular dynamic simulations
(2020-05-28)
Yue, Ling
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Yu, Le
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Xu, Chao
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Zhu, Chaoyuan
;
Liu, Yajun
The global nonadiabatic switching on-the-fly trajectory surface hopping simulation at the 8SA-CASSCF quantum level has been performed to estimate the quantum yield of chemiexcitation for the uncatalyzed decomposition reaction of the open-shell biradical trans-3,4-dimethyl-1,2-dioxetane system. The present ab initio nonadiabatic molecular dynamic simulation involving both conical intersection and intersystem crossing is to compute for the first time the population evolution of quantum yields at the four lowest singlet and four lowest triplet states. The simulated results demonstrate not only the stepwise dissociation of O-O and C-C bond breaking, but also confirm the existence of a biradical entropic trap which is responsible for chemiexcitation. The simulated quantum yield of the triplet chemiexcitation phi(T1) = 0.266 +/- 0.096 agrees with the experimental value of 0.20 +/- 0.04 very well. The present nonadiabatic molecular dynamic simulation of dimethyl 1,2-dioxetanes provides a further advanced understanding and stepping stone for future studies on chemi- and bio-luminescence.
Trajectory-based nonadiabatic molecular dynamics without calculating nonadiabatic coupling in the avoided crossing case: trans <-> cis photoisomerization in azobenzene
(2014-01-01)
Yu, Le
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Xu, Chao
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Lei, Yibo
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Zhu, Chaoyuan
;
Wen, Zhenyi
We develop a novel method to simulate analytical nonadiabatic switching probability based on effective coupling and effective collision energy by using only electronic adiabatic potential energy surfaces and its gradients in the case of avoided crossing types of nonadiabatic transitions. In addition, the present method can keep the same time step for computing both on-the-fly trajectory and nonadiabatic transitions accurately. The present method is most useful for localized nonadiabatic transitions induced by conical intersection. We employ the on-the-fly surface hopping algorithm with an ab initio quantum chemistry calculation to demonstrate a dynamic simulation for photoisomerization in azobenzene. Simulated quantum yield and lifetime converge to 0.39 and 53 femtosecond, respectively (0.33 and 0.81 picosecond) for cis-to-trans (trans-to-cis) photoisomerization with up to 800 (600) sampling trajectories. The present results agree well with those of the experiment, as well as results simulated with use of nonadiabatic coupling within Tully\'s fewest switching method. The present trajectory-based nonadiabatic molecular dynamics free from nonadiabatic coupling greatly enhances the simulation power of molecular dynamics for large complex chemical systems.