Browsing by Author "Li, Qian"

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Anharmonic Effect of N-Propyl Peroxy Dissociation
(2016-12)
Song, Liguo
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Pan, Xinxiang
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Li, Qian
;
Ding, Yang
;
Yao, Li
The anharmonic and harmonic dissociation rate constants of alkylperoxy (RO2) in different pathways, as well as those for the reactions of the n-propyl peroxy radical, were calculated using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. When the temperature/total energy increased, the rate constants of the different pathways varied independently, causing changes in the dominating/leading products. Anharmonic rate constants were larger than harmonic rate constants, and their difference increased with increasing temperature/energy. Therefore, the anharmonic effect cannot be neglected. The rate-determining steps of CH3CH2CH2OO dissociation are discussed. Then the anharmonic effect was found clearly for CH3CH2CH2OO dissociation, especially for the hydroperoxyalkyl radical (QOOH) dissociation. At low temperature, the rate constants were similar to those found from experiment, which indicated the RRKM theory was suitable for calculating the dissociation rates of RO2 species.
Anharmonic Effect of N-Propyl Peroxy Dissociation
(2016-12)
Song, Liguo
;
Pan, Xinxiang
;
Li, Qian
;
Ding, Yang
;
Yao, Li
The anharmonic and harmonic dissociation rate constants of alkylperoxy (RO2) in different pathways, as well as those for the reactions of the n-propyl peroxy radical, were calculated using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. When the temperature/total energy increased, the rate constants of the different pathways varied independently, causing changes in the dominating/leading products. Anharmonic rate constants were larger than harmonic rate constants, and their difference increased with increasing temperature/energy. Therefore, the anharmonic effect cannot be neglected. The rate-determining steps of CH3CH2CH2OO dissociation are discussed. Then the anharmonic effect was found clearly for CH3CH2CH2OO dissociation, especially for the hydroperoxyalkyl radical (QOOH) dissociation. At low temperature, the rate constants were similar to those found from experiment, which indicated the RRKM theory was suitable for calculating the dissociation rates of RO2 species.
Anharmonic effect of the unimolecular dissociation of CH3COOH
(2014-11-02)
Zhang, Liwei
;
Yao, Li
;
Li, Qian
;
Wang, Guiqiu
;
Lin, S. H.
Anharmonic and harmonic rate constants of the reactions have been calculated with the Rice-Ramsperger-Kassel-Marcus theory, and the anharmonic results are higher than the harmonic ones. The anharmonic effect and isotopic effect on the decomposition reactions have also been examined. The anharmonic effect in all the four reactions is obvious, especially at the high temperatures or energies. Relatively, the anharmonic effect on the reaction trans-acetic acid -> TS2 radical is the least obvious among the four reactions. In the microcanonical system, the difference of the rate constants between the deuterated results and the non-deuterated results is not negligible; in other words, the isotopic effect is obvious in all the four reactions. Among these reactions, three of the deuterated results (d, d3 and d4) have a big difference.
Anharmonic effect of the unimolecular dissociation of Glycerol to Glycidol
(2018-09-01)
Li, Qian
;
Yao, Li
;
Lin, S. H.
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應用化學系
;
Department of Applied Chemistry
The unimolecular dissociation rate constants of the dehydration of Glycerol to Glycidol were calculated at the MP2/6-311G(d,p) level using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The anharmonic effect of the reactions was examined by comparing the rate constants at temperatures (700-3000 K) of the canonical case and total energies (25654-53089 cm(-1)) of the microcanonical system. The calculations showed that high temperatures are required for the reaction to proceed. As the temperatures and total energies increased, the rate of reactions increased. However, the growth rate of the unimolecular dissociation rate constants was high and slower both in the canonical and microcanonical systems. Comparative analysis showed that the anharmonic effect was most significant for the reaction C -> TSC -> IV + H2O and least significant for the reaction B -> TSB1 -> I + H2O. The anharmonic effect became more significant as the temperatures and total energies increased. Compared with the microcanonical situation, the anharmonic effect of the canonical system was more pronounced.
Anharmonic Effect of the Unimolecular Dissociation of HFCO and DFCO
(2015-07-01)
Zhong, Jingjun
;
Wang, Weiwen
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Li, Qian
;
Xia, Wenwen
;
Shao, Ying
The unimolecular reactions of HFCO and DFCO have been studied by RRKM theory. The harmonic and anharmonic rate constants of the HFCO and DFCO decompositions have been calculated. The harmonic and anharmonic rate constants increase with the increasing temperatures and total energies both in the canonical and microcanonical systems. The comparison shows that the rate constants of DFCO decomposition are lower than that of the HFCO decomposition. The anharmonic effect and isotope effect have also been investigated. It has been found that the anharmonic effect and isotope effect are not significant either in the canonical or microcanonical system for all the reactions.
Anharmonic Effect of the Unimolecular Isomerization/Decomposition of Benzyne
(2015-04-01)
Li, Qian
;
Yao, Li
;
Lin, S. H.
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應用化學系
;
Department of Applied Chemistry
The anharmonic and harmonic rate constants were calculated for the unimolecular decomposition of o-benzyne, the isomerization of o-benzyne to m-benzyne, the isomerization of m-benzyne to p-benzyne and unimolecular decomposition of p-benzyne by using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory respectively, in the canonical and microcanonical systems. The geometry and the vibrational frequencies were calculated by MP2 and B3LYPmethods with 6-311G(d,p) basis set and the barrier energies were corrected using CBS-QB3 theory. The anharmonic effect on the reactions was also examined. Comparison of results for the decompositions of benzyne indicate that both in microcanonical and canonical cases, the anharmonic effect on the decomposition of the o-C6H4 and p-C6H4 are significant, while the anharmonic effect on the two isomerizations are not pronounced.
Calculation of anharmonic effect on the dissociation of ethylene glycol
(2017-12-01)
Li, Qian
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Yao, Li
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Lin, S. H.
;
應用化學系
;
Department of Applied Chemistry
The unimolecular dissociation rate constants of ethylene glycol were examined using the MP2/6-311++G(d, p) method based on the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The effect of anharmonicity on the dissociation rate constants was evaluated at 500-4000 K temperatures of the canonical system and 25,182-50,235 cm(-1) total energies of the microcanonical system. The comparison of the results showed that the H2O elimination reaction played a critical role in the decomposition processes of ethylene glycol. The results of the rate constant calculations indicated that the H2O elimination reaction dominated at low temperatures, whereas the direct C-C bond dissociation reaction (CH2OHCH2OH -> CH2OH+CH2OH) dominated at high temperatures. For channel 1, CH2OH+CH2OH, the anharmonic effect of the canonical system was not observed, while it became more obvious with the increasing total energies in the microcanonical system. For channels 2-5, CH3CHO+H2O, CH2CHOH+H2O, CH3OH+CHOH, and CH2OHCHO+H-2, the anharmonic effect of canonical and microcanonical systems became more obvious with increasing temperatures and total energies. The comparison showed that, for channels 1 and 4, C-C bond dissociation and the anharmonic effect of the microcanonical system were more evident, whereas the anharmonic effect of the canonical system was more predominant for channels 2 (CH3CHO+H2O), 3 (CH2CHOH+H2O), and 5 (CH2OHCHO+H-2).
Calculation of anharmonic effects for the unimolecular dissociation of CH3OOH and its deuterated species CD3OOD using the Rice-Ramsperger-Kassel-Marcus theory
(2015-06-01)
Li, Qian
;
Yao, Li
;
Lin, S. H.
;
應用化學系
;
Department of Applied Chemistry
Anharmonic and harmonic rate constants for the unimolecular dissociation of CH3OOH and CD3OOD were calculated using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory at the MP2/6-311++G(3df,3pd) level of theory. The anharmonic effect of the reactions was investigated. Comparison of results for the decompositions of CH3OOH and CD3OOD shows that the direct bond dissociation channel, CH3 (D-3) O + OH (D), is the most dominant reaction. The anharmonic effect plays an important role in the unimolecular dissociation of both CH3OOH and CD3OOD. For channels CH3 (D-3) O + OH (D) and CH3 (D-3) + H (D) O-2, the anharmonic effect of the unimolecular dissociation of CD3OOD is more pronounced than that of the unimolecular dissociation of CH3OOH. For channel H-2 (D-2) CO + H-2 (D-2) O, the anharmonic effect of the unimolecular dissociation of CH3OOH is more pronounced than that of the unimolecular dissociation of CD3OOD. The isotope effect is more distinct in the anharmonic oscillator model.
Calculation of anharmonic effects in the unimolecular dissociation of M2+ (H2O)(2) (M = Be, Mg, and Ca)
(2015-11-17)
Li, Qian
;
Yao, Li
;
Xia, Wenwen
;
Lin, S. H.
;
應用化學系
The anharmonic and harmonic rate constants of the unimolecular dissociation of M2+(H2O)(2) (M = Be, Mg, and Ca) were calculated using the Rice-Ramsperger-Kassel-Marcus theory. The anharmonic effects of the reactions were investigated. The results show that the energy barrier of the dissociation of Be2+(H2O)(2) is 68.47 kcal/mol, and the anharmonic (T-4000K = 4.28x10(8) s(-1)) and harmonic (T-4000K = 4.22x10(8) s(-1)) rate constants were close in value in both the canonical and microcanonical systems. The energy barriers of the two steps for the dissociation, Mg2+(H2O)(2) MgOH++H3O+, were 37.41 and 11.39 kcal/mol, and those for the dissociation, Ca2+(H2O)(2) CaOH++H3O+, were 21.15 and 26.42 kcal/mol. The anharmonic effect of the two reactions is significant and cannot be neglected in both the canonical and microcanonical systems. The comparison also shows that the rate constants of the dissociation of Ca2+(H2O)(2) have the maximum values, while those of Be2+(H2O)(2) have the minimum values in the three reactions; however, the anharmonic effect also shows the similar trend in the comparison.
Complex strain evolution of polar and magnetic order in multiferroic BiFeO3 thin films
(2018-09-21)
Chen, Zuhuang
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Chen, Zhanghui
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Kuo, Chang-Yang
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Tang, Yunlong
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Dedon, Liv R.
Electric-field control of magnetism requires deterministic control of the magnetic order and understanding of the magnetoelectric coupling in multiferroics like BiFeO3 and EuTiO3. Despite this critical need, there are few studies on the strain evolution of magnetic order in BiFeO3 films. Here, in (110)-oriented BiFeO3 films, we reveal that while the polarization structure remains relatively unaffected, strain can continuously tune the orientation of the antiferromagnetic-spin axis across a wide angular space, resulting in an unexpected deviation of the classical perpendicular relationship between the antiferromagnetic axis and the polarization. Calculations suggest that this evolution arises from a competition between the Dzyaloshinskii-Moriya interaction and single-ion anisotropy wherein the former dominates at small strains and the two are comparable at large strains. Finally, strong coupling between the BiFeO3 and the ferromagnet Co0.9Fe0.1 exists such that the magnetic anisotropy of the ferromagnet can be effectively controlled by engineering the orientation of the antiferromagnetic-spin axis.
Miscible density-driven flows in heterogeneous porous media: Influences of correlation length and distribution of permeability
(2019-01-04)
Li, Qian
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Cai, Weihua
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Li, Feng-Chen
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Li, Bingxi
;
Chen, Ching-Yao
A random process and highly accurate pseudospectral method associated with compact finite differences are incorporated to evaluate effects of permeability heterogeneity to gravity-driven miscible porous media flows. Flows in heterogeneous permeability fields, based on multiple sets of random realizations with identical statistical characteristics, are simulated to elucidate the global trend of mean quantities and local variations. The presence of heterogeneity provokes more prominent fingering competition and greater variation of fingers' widths, hence the mean values of interested quantitative measures, i.e., breakthrough time, amount of fluid volumes transported, and normalized mixing effectiveness, are generally reduced. Resonant effects, whose influences on the flow fields are the most significant, are verified to occur in an intermediate correlation length, in which the widths of fingers are slightly less than the correspondent correlation length. Nevertheless, under the resonant conditions these measures are the most widely scattered between different random realizations associated with the same control parameters. The widest scatterings are mainly because of the enhancing sensitivity of flow path selections under such resonant conditions, especially in a few realizations whose high or low permeability regions align along with or transverse to the main flow direction. The significant scatterings of these quantitative measures, which had drawn little attention previously, suggest more cautious treatments for practical implementations in the regime of resonant effects.
Numerical study of immiscible viscous fingering in chemically reactive Hele-Shaw flows: Production of surfactants
(2019-10-16)
Tsuzuki, Reiko
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Li, Qian
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Nagatsu, Yuichiro
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Chen, Ching-Yao
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機械工程學系
Viscous fingering on chemically reactive and immiscible interface is simulated by the phase-field method. The reaction produces surfactants on the interface to reduce local interfacial tension. Parametric analysis regarding the influences of reaction, determined by the dimensionless Damkohler number (Da) and the saturated capillary coefficient (epsilon(s)), on the fingering prominence at a prescribed breakthrough time is presented. The injection rate and viscosity ratio are also varied to observe their influences on the patterns. Transported by the fountain flows formed in the fingers, the produced surfactants tend to accumulate on the sides of fingers to weaken the local interfacial tension so that great variation of capillary effect will exist along the interface, especially for an intermediate range of Da. The weaker local capillary effect on a finger's side could result in prominent side-branching instability. Nonmonotonic behavior regarding the prominence of fingering instability for continuously increased injection flow rate observed in experiments is confirmed and explained qualitatively by the simulations. A reference capillary number (Ca-R) is proposed which is capable to monotonically describe the viscous fingering associated with both temporal and spatial changes of interfacial tension by reaction.
Study on Anharmonic Effect of the Unimolecular Reaction of CH2(D-2)FO
(2014-12-20)
Zhong, Jingjun
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Li, Qian
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Luo, Ji
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Xia, Wenwen
;
Yao, Li
Study on the unimolecular reaction for CH2FO and CD2FO is carried out. The structures, energy barriers and zero point energy of the three channels in the title unimolecular reactions are computed with the MP2/6-311++G(3df, 3pd) method. RRKM theory is used to calculate the rate constants of canonical case at temperature range of 500-5000 K and microcanonical system at total energy of 19.05-71.68 kcal/mol. The results indicate that the anharmonic effect and isotope effect are very small for the three channels, and the anharmonic rate constants, around 10(9)-10(11) s(-1), are close to the experimental prediction reasonably.
The impact of heterogeneous anisotropy of porous media on density-driven convection
(2019-09-26)
Li, Qian
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Cai, Weihua
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Tang, Xiaojing
;
Chen, Yicheng
;
Li, Bingxi
Purpose The aim of this study is to numerically simulate the density-driven convection in heterogeneous porous media associated with anisotropic permeability field, which is important to the safe and stable long term CO2 storage in laminar saline aquifers. Design/methodology/approach The study uses compact finite difference and the pseudospectral method to solve Darcy's law. Findings The presence of heterogeneous anisotropy may result in non-monotonic trend of the breakthrough time and quantity of CO2 dissolved in the porous medium, which are important to the CO2 underground storage. Originality/value The manuscript numerically study the convective phenomena of mixture contained CO2 and brine. The phenomena are important to the process of CO2 enhanced oil recovery. Interesting qualitative patterns and quantitative trends are revealed in the manuscript.