Browsing by Author "Gu, Feng Long"

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A Density Functional Theory Study on Nonlinear Optical Properties of Double Cage Excess Electron Compounds: Theoretically Design M[Cu(Ag)@(NH3)(n)](M = Be, Mg and Ca; n=1-3)
(2019-04-05)
Liang, Yan Ying
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Li, Bo
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Xu, Xuan
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Gu, Feng Long
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Zhu, Chaoyuan
In this work, we investigated the nonlinear optical (NLO) properties of excess electron electride molecules of M[Cu(Ag)@(NH3)(n)](M = Be, Mg and Ca; n = 1-3) using density functional theory (DFT). This electride molecules consist of an alkaline-earth (Be, Mg and Ca) together with transition metal (Cu and Ag) doped in NH3 cluster. The natural population analysis of charge and their highest occupied molecular orbital suggests that the M[Cu(Ag)@(NH3)(n)] compound has excess electron like alkaline-earth metal form double cage electrides molecules, which exhibit a large static first hyperpolarizability (beta(e)(0)) (electron contribution part) and one of which owns a peak value of beta(e)(0) 216,938 (a.u.) for Be [Ag@(NH3)(2)] and vibrational harmonic first hyperpolarizability [(beta(nr)(zzz)) (nuclear contribution part) values and the ratio of beta(nr)(zzz)/beta(e)(zzz'), namely, eta values from 0.02 for Be[Ag@(NH3)] to 0.757 for Mg [Ag@(NH3)(3)]. The electron density contribution in different regions on beta(e)(zzz) values mainly come from alkaline-earth and transition metal atoms by first hyperpolarizability density analysis, and also explains the reason why beta(e)(zzz) values are positive and negative. Moreover, the frequency-dependent values ss(-2 omega,omega,omega) are also estimated to make a comparison with experimental measures. (c) 2018 Wiley Periodicals, Inc.
A nonlinear optical switch induced by an external electric field: inorganic alkaline-earth alkalide
(2019-05-28)
Li, Bo
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Peng, Daoling
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Gu, Feng Long
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Zhu, Chaoyuan
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應用化學系分子科學碩博班
Exploring a new type of nonlinear optical switch molecule with excess electron character is extremely important for promoting the application of excess electron compounds in the nonlinear optical (NLO) field. Here, we report external electric field (EEF) induced second-order NLO switch molecules of inorganic alkaline-earth alkalides, M(NH3) 6Na2 (M = Mg or Ca). The centrosymmetric structure of M(NH3) 6Na2 is destroyed in the presence of an EEF, and then a long-range charge transfer process occurs. It has been found that excess electrons are gradually transferred from one Na atom to the other Na atom through the inorganic metal cluster M(NH3) 6. Finally, the excess electrons are completely located on one of the two Na atoms. In particular, the electronic contribution of the static first hyperpolarizability (b e 0) for M(NH3) 6Na2 exhibits a large significant difference when the EEF is switched on. The b e 0 value of M(NH3) 6Na2 is 0 when EEF = 0, while the peak b e 0 values are 5.95 106 (a. u.) for Mg(NH3) 6Na2 (EEF = 58 10 4 (a. u.)) and 1.83 107 (a. u.) for Ca(NH3) 6Na2 (EEF = 53 10 4 (a. u.)). This work demonstrates that the compounds M(NH3) 6Na2 can serve as potential candidates for NLO switches.
An excited-state Wolff rearrangement reaction of 5-diazo Meldrum's acid: an ab initio on-the-fly nonadiabatic dynamics simulation
(2018-09-21)
Xu, Chao
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Gu, Feng Long
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Zhu, Chaoyuan
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交大名義發表
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應用化學系
A global switching on-the-fly trajectory surface hopping dynamics simulation at the 3SA-CASSCF(12,11)/6-31G* quantum level has been employed to probe the photo-induced Wolff rearrangement (WR) reaction of 5-diazo Meldrum's acid (DMA) within three low-lying electronic excited states. The present simulation predicted that the branching ratios for relaxing back to the ground state, isomerizing to diazirine, and reaction to ketene I via carbene I are 69% +/- 0.1, 3% +/- 0.4, and 28% +/- 0.1, which are in excellent agreement with those obtained by the femtosecond spectroscopy experiment, 67%, 3% and 30%, respectively. In particular, the present simulation revealed that the major WR reaction to ketene I pathway is stepwise via the excited-state to carbene I (17.8% +/- 0.2) and via the ground-state to carbene I (8.7% +/- 0.2), and the minor pathway is concerted synchronous (1.5% +/- 0.6). The photo-induced WR reaction of DMA has been quantitatively interpreted in terms of the distribution of extended seam surfaces as a function of CN dissociation bonds for two important conical intersections within three low-lying electronic excited states. Ultrafast dynamic time constants have been estimated to be about 500 fs +/- 120 fs and 180 fs +/- 80 fs for the stepwise and the concerted WR reaction to ketene I which are also in good agreement with those determined by the experiment. Therefore, the photo-induced excited-state WR reaction mechanism has been quantitatively revealed by the present real-time dynamics simulation.
Facially Polarized Molecule for Alkalides and Superalkalides with Considerable Nonlinear Optical Response
(2018-12-06)
Li, Bo
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Peng, Daoling
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Gu, Feng Long
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Zhu, Chaoyuan
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應用化學系
In this work, alkali M (Li and K) and superalkali M ' O-3 (M '=Li and Na) combined with facially polarized molecule, all-cis 1,2,3,4,5,6-Hexafluorocyclohexane (L, C6H6F6), were utilized to design novel alkalides L-M-L-M ' and superalkalides L-M-L-M ' O-3, respectively. Computational results show that alkalides L-M-L-M ' and superalkalides L-M-L-M ' O-3 have high thermodynamic stability, and the superalkalides L-M-L-M ' O-3 are more stable than the alkalides L-M-L-M '. Importantly, they also possess remarkable NLO responses, the electronic contribution of the static first hyperpolarizability (beta(e)(0)) has upped to 3.42x10(6) (a.u.) for L-K-L-Li3O. In particularly, the number of ligand L considerably impacts on beta(e)(0) value, namely, the beta(e)(0) value of Li-L-Li3O can be improved two orders of magnitude by adding additional ligand L, 1.31x10(6) (a.u.)(L-Li-L-Li3O) > 7.76x10(4) (a.u.)(Li-L-Li3O). We hope this work can attract researchers to design and synthesize novel excess electron compounds with high performance NLO materials.
Functional and Basis Set Dependence for Time-Dependent Density Functional Theory Trajectory Surface Hopping Molecular Dynamics: Cis-Azobenzene Photoisomerization
(1970-01-01)
Ye, Linfeng
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Xu, Chao
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Gu, Feng Long
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Zhu, Chaoyuan
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交大名義發表
Within three functionals (TD-B3LYP, TD-BHandHLYP, and TD-CAM-B3LYP) in combination with four basis sets (3-21g, 6-31g, 6-31g(d), and cc-pvdz), global switching (GS) trajectory surface hopping molecular dynamics has been performed for cis-to-trans azobenzene photoisomerization up to the S-1(n pi*) excitation. Although all the combinations show artificial double-cone structure of conical intersection between ground and first excited states, simulated quantum yields and lifetimes are in good agreement with one another; 0.6 (+/- 5%) and 40.5 fs (+/- 10%) by TD-B3LYP, 0.5 (+/- 10%) and 35.5 fs (+/- 4%) by TD-BHandHLYP, and 0.44 (+/- 9%) and 35.2 fs (+/- 10%) by TD-CAM-B3LYP. By analyzing distributions of excited-state population decays, hopping spots, and typical trajectories with performance of 12 functional/basis set combinations, it has been concluded that functional dependence for given basis set is slightly more sensitive than basis set dependence for given functional. The present GS on-the-fly time-dependent density functional theory (TDDFT) trajectory surface hopping simulation can provide practical benchmark guidelines for conical intersection driven excited-state molecular dynamics simulation involving in large complex system within ordinary TDDFT framework. (c) 2019 Wiley Periodicals, Inc.
Insight into the Expanded Mislinked Porphyrins with High Second Order Nonlinear Optical Response
(2020-02-06)
Li, Bo
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Sathishkumar, Palanivel
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Gu, Feng Long
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Zhu, Chaoyuan
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應用化學系
Materials with outstanding nonlinear optical (NLO) response exhibit excellent prospects in electrooptic devices. Thus, it is essential to find a high-performance NLO material to meet the growing demand for high-speed data transmission. In this study, theoretical investigations on the second order NLO properties of the novel expanded mislinked thia-norhexaphyrin, sulfur-free pentaphyrin, and their substituted derivatives were performed using density functional theory. Theoretical calculations display that the approximate planar structures of sulfur-free pentaphyrin embedded with two five-membered rings exhibits a remarkable NLO response and holds large dipolar contribution (Phi(J=1) = 63.5%) to the first hyperpolarizability among four parent expanded mislinked porphyrins. The static first hyperpolarizability values of these expanded porphyrins were found to range from 3490 to 14 229 au. In addition, the second order NLO response of these porphyrins has greatly improved except for minority electron-releasing- and electron-withdrawing-group substituted cases, and the static first hyperpolarizability value has increased to 47 950 au after installing the donor and acceptor groups. Unambiguous evidence reveals that expanded mislinked porphyrin can serve as a potential candidate for NLO materials.
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
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Yu, Le
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Gu, Feng Long
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Zhu, Chaoyuan
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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.
Remarkable nonlinear optical response of excess electron compounds: theoretically designed alkali-doped aziridine M-(C2NH5)(n)
(2017-09-21)
Li, Bo
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Xu, Chao
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Xu, Xuan
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Zhu, Chaoyuan
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Gu, Feng Long
Theoretically designed alkali-doped aziridine M-(C2NH5)(n) (M = Li, Na and K; n = 1, 2, 3, and 4) are investigated by density functional theory (DFT) and time-dependent TD-DFT. The interaction energies at optimized electronic structures indicate that alkali-doped aziridine are quite stable. The natural population analysis of charges on alkali atoms show that all positive and electronic transitions to LUMO orbitals are large, so that the designed compounds not only have electride features, but also have large flexible ligands. This leads to a high-performance nonlinear optical response (NLO) and this remarkable NLO response mainly comes from alkali atoms. By calculating the first hyperpolarizabilities for M-(C2NH5)(4) with M@ Calix[4] pyrrole for comparison, we demonstrate that enhancements of the NLO response of M-(C2NH5)(4) are 10 to 100 times larger than those of M@ Calix[ 4] pyrrole, and in particular, the largest first hyperpolarizability values of Na-(C2NH5)(4) is up to 3.4 x 10(6) (a. u.).
Ultrafast intersystem crossing for nitrophenols: ab initio nonadiabatic molecular dynamics simulation
(2018-02-28)
Xu, Chao
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Gu, Feng Long
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Zhu, Chaoyuan
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應用化學系
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應用化學系分子科學碩博班
Ultrafast intersystem crossing mechanisms for two p- and m-nitrophenol groups (PNP and MNP) have been investigated using ab initio nonadiabatic molecular dynamics simulations at the 6SA-CASSCF level of theory. Trajectory surface hopping simulation has been performed within an intersystem crossing network constructed from two low-lying singlets (S-0 and S-1) and two low-lying triplets (T-1 and T-2). It is found that the dominant relaxation S-1 -> T-2 pathway accounts for 65.4% (85.0%) of the quantum yield with a time constant of 13.4 fs (22 fs) and the S-1 -> T-2 -> S-0 pathway accounts for 33.1% (13.5%) with a time constant of 275 fs ( 375 fs) for PNP ( MNP). In comparison with the previously studied excited-state proton transfer process for ONP, the dominant relaxation S-1 -> T-2 -> T-1 pathway accounts for 49.3% with a time constant of 40 fs and the S-1 -> T-2 -> T-1 -> S-0 pathway accounts for 47.5% with a time constant of 300 fs. The relaxation mechanisms and electronic structures of the intersystem crossings are in close relation with the relative motion between the torsion motions of the nitro-group and the hydroxyl group. The present simulation provides new physical insight for understanding ultrafast photochemical intersystem crossing dynamics.