Browsing by Author "Liu, Yajun"

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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.
Performance of TDDFT with and without spin-flip in trajectory surface hopping dynamics: cis-trans azobenzene photoisomerization
(2018-10-07)
Yue, Ling
;
Liu, Yajun
;
Zhu, Chaoyuan
;
交大名義發表
;
應用化學系
Time-dependent density functional theory (TDDFT) with and without a spin-flip scheme is extensively compared in on-the-fly trajectory surface hopping molecular dynamics with a global switching (GS) algorithm. The simulation is performed for cis-trans azobenzene photoisomerization following the excitation to the S-1(n pi*) state that is involved in a conical intersection (CI) between ground and first excited states. This CI is found correctly to be a single-cone (artificial double-cone) structure computed by the TDDFT method with (and without) spin-flip. Nevertheless, simulated quantum yields and lifetimes are in very good agreement; 0.43 and 63 fs (0.34 and 62 fs) for cis-to-trans isomerization, and 0.11 and 2200 fs (0.13 and 1040 fs) for trans-to-cis isomerization, by TDDFT with (and without) a spin-flip scheme. Distributions of excited-state decay, hopping spots and products, as well as typical trajectories have similar patterns and behaviors with and without spin-flip. The global switching trajectory surface hopping method is demonstrated to be well suited to TDDFT on-the-fly dynamic simulation with and without spin-flip. For comparison, previous simulations with the CASSCF method and Tully's fewest-switches trajectory surface hopping method are also addressed.
Quantum yields of singlet and triplet chemiexcitation of dimethyl 1,2-dioxetane: ab initio nonadiabatic molecular dynamic simulations
(2020-05-28)
Yue, Ling
;
Yu, Le
;
Xu, Chao
;
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.