Browsing by Author "Lei, Yibo"

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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
;
Yu, Le
;
Xu, Chao
;
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
;
Yu, Le
;
Zheng, Xiaolei
;
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.
Constraint Trajectory Surface-Hopping Molecular Dynamics Simulation of the Photoisomerization of Stilbene
(2014)
Lei, Yibo
;
Wu, Shaomei
;
Zhu, Chaoyuan
;
Wen, Zhenyi
;
Lin, Sheng-Hsien
Combining trajectory surface hopping (TSH) method with constraint molecular dynamics, we have extended TSH method from full to flexible dimensional potential energy surfaces. Classical trajectories are carried out in Cartesian coordinates with constraints in internal coordinates, while nonadiabatic switching probabilities are calculated separately in free internal coordinates by Landau-Zener and Zhu-Nakamura formulas along the seam. Two-dimensional potential energy surfaces of ground S-0 and excited S-1 states are constructed analytically in terms of torsion angle and one dihedral angle around the central ethylenic C-C bond, and the other internal coordinates are all fixed at configuration of the conical intersection. At this conical intersection, the branching ratio from the present simulation is 48 : 52 (33 : 67) initially starting from trans(cis)-Stilbene in comparison with experimental value 50 : 50. Quantum yield for trans-to-cis isomerization is estimated as 49% in very good agreement with experimental value of 55%, while quantum yield for cis-to-trans isomerization is estimated as 47% in comparison with experimental value of 35%.
Excited-state E -> Z photoisomerization mechanism unveiled by ab initio nonadiabatic molecular dynamics simulation for hemithioindigo-hemistilbene
(2017-05-21)
Yang, Meihong
;
Huo, Chunyan
;
Li, Anyang
;
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.
Landscapes of Four-Enantiomer Conical Intersections for Photoisomerization of Stilbene: CASSCF Calculation
(2014-10-02)
Lei, Yibo
;
Yu, Le
;
Zhou, Bo
;
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
;
Chen, Juan
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Yu, Le
;
Li, Anyang
;
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.
Photo-induced 1,3-cyclohexadiene ring opening reaction: Ab initio on-the-fly nonadiabatic molecular dynamics simulation
(2016-02-15)
Lei, Yibo
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Wu, Huiyu
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Zheng, Xiaolei
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Zhai, Gaohong
;
Zhu, Chaoyuan
By a newly developed algorithm to compute global nonadiabatic switching probability only using electronic adiabatic potential energy surfaces and its gradients, we could able to perform on-the-fly trajectory surface hopping molecular dynamics at the SA-CASSCF(14, 8)/6-31G* quantum level to investigate the photo-induced 1,3-cyclohexadiene ring opening reaction from 1,3-cyclohexadiene (CHD) to 1,3,5-hexatriene (HT). We found four conical intersection zones within three singlet low-lying electronic states, in which 1B/2A and 1A/2A are well known to be the most important conical intersection zones to govern dynamics of ring opening reaction. The present simulation gained insight into nonadiabatic dynamics in which 516 sampling trajectories out of 600 can switch back and forth between two involved potential energy surfaces not only at 1B/2A, but also at 1A/2A. This insight is the key to influence quantum yields and time scales of the ring opening reaction. We estimated time constants as 46 fs, 82 fs, and 120 fs, respectively for crossing 1B/2A and 1A/2A, and excited-state lifetime in comparison with corresponding experimental values 56 fs, 80 fs and 130 fs. We estimated quantum yield 0.47/0.53 to HT/CHD in comparison to experiment values 0.30/0.70 in the gas-phase and 0.41/0.59 in the condense-phase. Moreover, the present simulation within 600 sampling trajectories indicates that there is no five membered ring forming in agreement with experiment results and with prediction from the previous wave-packet simulation as a rare case. (C) 2015 Elsevier B.V. All rights reserved.
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
;
Zhai, Gaohong
;
Gao, Wanqing
;
Lei, Yibo
;
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.
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
;
Yu, Le
;
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.
Trajectory-based nonadiabatic molecular dynamics without calculating nonadiabatic coupling in the avoided crossing case: trans <-> cis photoisomerization in azobenzene
(2014-01-01)
Yu, Le
;
Xu, Chao
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Lei, Yibo
;
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.