1
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Wei Z, Xu H, Xu X, Feng G, Zheng W, Li T. Solvation of magnesium chloride dimer in water: The case of anionic and neutral clusters. J Chem Phys 2023; 158:2888211. [PMID: 37140000 DOI: 10.1063/5.0146319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2023] [Accepted: 04/24/2023] [Indexed: 05/05/2023] Open
Abstract
The structures of magnesium chloride dimer-water clusters, (MgCl2)2(H2O)n-/0, were investigated with size-selected anion photoelectron spectroscopy and theoretical calculations to understand the dissolution of magnesium chloride in water. The most stable structures were confirmed by comparing vertical detachment energies (VDEs) with the experimental measurements. A dramatic drop of VDE at n = 3 has been observed in the experiment, which is in accordance with the structural change of (MgCl2)2(H2O)n-. Compared to the neutral clusters, the excess electron induces two significant phenomena in (MgCl2)2(H2O)n-. First, the planar D2h geometry can be converted into a C3v structure at n = 0, making the Mg-Cl bonds easier to be broken by water molecules. More importantly, a negative charge-transfer-to-solvent process occurs after adding three water molecules (i.e., at n = 3), which leads to an obvious deviation in the evolution of the clusters. Such electron transfer behavior was noticed at n = 1 in monomer MgCl2(H2O)n-, indicating that the dimerization between two MgCl2 molecules can make the cluster more capable of binding electron. In neutral (MgCl2)2(H2O)n, this dimerization provides more sites for the added water molecules, which can stabilize the entire cluster and maintain its initial structure. Specifically, filling the coordination number to be 6 for Mg atoms can be seen as a link between structural preferences in the dissolution of the monomers, dimers, and extended bulk-state of MgCl2. This work represents an important step forward into fully understanding the solvation of MgCl2 crystals and other multivalent salt oligomers.
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Affiliation(s)
- Zhiyou Wei
- Wenzhou Institute, University of Chinese Academy of Sciences, Wenzhou, Zhejiang 325001, China
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Hongguang Xu
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xiling Xu
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Gang Feng
- Department of Chemistry, School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, China
| | - Weijun Zheng
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Tao Li
- Wenzhou Institute, University of Chinese Academy of Sciences, Wenzhou, Zhejiang 325001, China
- Oujiang Laboratory (Zhejiang Lab for Regenerative Medicine, Vision and Brain Health), Wenzhou, Zhejiang 325001, China
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2
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Wei ZY, Yang LJ, Gong SY, Xu HG, Xu XL, Gao YQ, Zheng WJ. Comparison of the Microsolvation of CaX 2 (X = F, Cl, Br, I) in Water: Size-Selected Anion Photoelectron Spectroscopy and Theoretical Calculations. J Phys Chem A 2021; 125:3288-3306. [PMID: 33872010 DOI: 10.1021/acs.jpca.1c00573] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To understand the microsolvation of alkaline-earth dihalides in water and provide information about the dependence of solvation processes on different halides, we investigated CaBr2(H2O)n-, CaI2(H2O)n-, and CaF2(H2O)n- (n = 0-6) clusters using size-selected anion photoelectron spectroscopy and conducted theoretical calculations on these clusters and their neutrals. The results are compared with those of CaCl2(H2O)n-/0 clusters reported previously. It is found that the vertical detachment energies (VDEs) of CaCl2(H2O)n-, CaBr2(H2O)n-, and CaI2(H2O)n- show a similar trend with increasing cluster size, while the VDEs of CaF2(H2O)n- show a different trend. The VDEs of CaF2(H2O)n- are much lower than those of CaCl2(H2O)n-, CaBr2(H2O)n-, and CaI2(H2O)n-. A detailed probing of the structures shows that a significant increase of the Ca-X distance (separation of Ca2+-X- ion pair) in CaCl2(H2O)n-/0, CaBr2(H2O)n-/0, and CaI2(H2O)n-/0 clusters occurred at about n = 5. However, for CaF2(H2O)n-/0, no abrupt change of the Ca-F distance with the increasing cluster size has been observed. In CaCl2(H2O)6-/0, CaBr2(H2O)6-/0, and CaI2(H2O)6-/0, the Ca atom coordinates directly with 5 H2O molecules. However, in CaF2(H2O)n-/0, the Ca atom coordinates directly with only 2 or 3 H2O molecules. The similarity or differences in the structures and coordination numbers are consistent with the fact that CaCl2, CaBr2, and CaI2 have similar solubility, while CaF2 has much lower solubility.
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Affiliation(s)
- Zhi-You Wei
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.,University of Chinese Academy of Sciences, Beijing 100049, China
| | - Li-Jiang Yang
- Beijing National Laboratory for Molecular Science, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Shi-Yan Gong
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.,University of Chinese Academy of Sciences, Beijing 100049, China
| | - Hong-Guang Xu
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.,University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xi-Ling Xu
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.,University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yi Qin Gao
- Beijing National Laboratory for Molecular Science, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.,Biomedical Pioneering Innovation Center, Peking University, Beijing 100871, China
| | - Wei-Jun Zheng
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.,University of Chinese Academy of Sciences, Beijing 100049, China
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3
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Vong A, Widmer DR, Schwartz BJ. Nonequilibrium Solvent Effects during Photodissociation in Liquids: Dynamical Energy Surfaces, Caging, and Chemical Identity. J Phys Chem Lett 2020; 11:9230-9238. [PMID: 33064478 DOI: 10.1021/acs.jpclett.0c02515] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
In the gas phase, potential energy surfaces can be used to provide insight into the details of photochemical reaction dynamics. In solution, however, it is unclear what potential energy surfaces, if any, can be used to describe even simple chemical reactions such as the photodissociation of a diatomic solute. In this paper, we use mixed quantum/classical (MQC) molecular dynamics (MD) to study the photodissociation of Na2+ in both liquid Ar and liquid tetrahydrofuran (THF). We examine both the gas-phase potential surfaces and potentials of mean force (PMF), which assume that the solvent remains at equilibrium with the solute throughout the photodissociation process and show that neither resemble a nonequilibrium dynamical energy surface that is generated by taking the time integral of work. For the photodissociation of Na2+ in liquid Ar, the dynamical energy surface shows clear signatures of solvent caging, and the degree of caging is directly related to the mass of the solvent atoms. For Na2+ in liquid THF, local specific interactions between the solute and solvent lead to changes in chemical identity that create a kinetic trap that effectively prevents the molecule from dissociating. The results show that nonequilibrium effects play an important role even in simple solution-phase reactions, requiring the use of dynamical energy surface to understand such chemical events.
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Affiliation(s)
- Andy Vong
- Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, United States
| | - Devon R Widmer
- Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, United States
| | - Benjamin J Schwartz
- Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, United States
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4
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Wei ZY, Yang LJ, Xu HG, Farooq U, Xu XL, Gao YQ, Zheng WJ. Hydration processes of barium chloride: Size-selected anion photoelectron spectroscopy and theoretical calculations of BaCl 2-water clusters. J Chem Phys 2020; 153:134301. [PMID: 33032412 DOI: 10.1063/5.0021991] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In order to understand the hydration processes of BaCl2, we investigated BaCl2(H2O)n - (n = 0-5) clusters using size-selected anion photoelectron spectroscopy and theoretical calculations. The structures of neutral BaCl2(H2O)n clusters up to n = 8 were also investigated by theoretical calculations. It is found that in BaCl2(H2O)n -/0, the Ba-Cl distances increase very slowly with the cluster size. The hydration process is not able to induce the breaking of a Ba-Cl bond in the cluster size range (n = 0-8) studied in this work. In small BaCl2(H2O)n clusters with n ≤ 5, the Ba atom has a coordination number of n + 2; however, in BaCl2(H2O)6-8 clusters, the Ba atom coordinates with two Cl atoms and (n - 1) water molecules, and it has a coordination number of n + 1. Unlike the previously studied MgCl2(H2O)n - and CaCl2(H2O)n -, negative charge-transfer-to-solvent behavior has not been observed for BaCl2(H2O)n -, and the excess electron of BaCl2(H2O)n - is mainly localized on the Ba atom rather on the water molecules. No observation of Ba2+-Cl- separation in current work is consistent with the lower solubility of BaCl2 compared to MgCl2 and CaCl2. Considering the BaCl2/H2O mole ratio in the saturated solution, one would expect that about 20-30 H2O molecules are needed to break the first Ba-Cl bond in BaCl2.
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Affiliation(s)
- Zhi-You Wei
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Li-Jiang Yang
- Beijing National Laboratory for Molecular Science, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Hong-Guang Xu
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Umar Farooq
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Xi-Ling Xu
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Yi-Qin Gao
- Beijing National Laboratory for Molecular Science, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Wei-Jun Zheng
- Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
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5
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Sun Z, Wang C, Zhao W, Zheng Y, Yang C. Control of photodissociation of the NaI molecule via pulse chirping. Phys Chem Chem Phys 2018; 20:20957-20962. [PMID: 30069561 DOI: 10.1039/c8cp02449a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A dynamic pump control scheme is proposed to manipulate the predissociation process of NaI molecules in different reaction channels. A linearly chirped pulse is used to excite the NaI molecule, and a time-delayed infrared pulse is employed to modify the molecular potentials in the coupling zone. The predissociation branching ratio of the product from two channels can be controlled by tuning the chirp rate with a proper range of delay times. Furthermore, an additional ultrafast photoionization step is adopted to monitor the wave packet evolution and probe the possible modifications of the electronic potential under the influence of a chirped pump field to reveal the physical mechanism behind the control. Aulter-Townes splitting is observed at a proper chirp rate, and the dressed-state population can be controlled via pulse chirping.
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Affiliation(s)
- Zhaopeng Sun
- School of Physics and Optoelectronic Engineering, Ludong University, Yantai 264025, China.
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6
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Rasskazov G, Nairat M, Magoulas I, Lozovoy VV, Piecuch P, Dantus M. Femtosecond real-time probing of reactions MMXVII: The predissociation of sodium iodide in the A 0+ state. Chem Phys Lett 2017. [DOI: 10.1016/j.cplett.2017.02.019] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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7
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Li RZ, Hou GL, Liu CW, Xu HG, Zhao X, Gao YQ, Zheng WJ. Initial hydration behavior of sodium iodide dimer: photoelectron spectroscopy and ab initio calculations. Phys Chem Chem Phys 2016; 18:557-65. [DOI: 10.1039/c5cp05550d] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We investigated (NaI)2−(H2O)n (n = 0–6) clusters to examine the initial solvation process of (NaI)2 in water, using negative ion photoelectron spectroscopy and theoretical calculations.
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Affiliation(s)
- Ren-Zhong Li
- College of Electronics and Information
- Xi'an Polytechnic University
- Xi'an 710048
- China
- Beijing National Laboratory for Molecular Sciences
| | - Gao-Lei Hou
- Beijing National Laboratory for Molecular Sciences
- State Key Laboratory of Molecular Reaction Dynamics
- Institute of Chemistry
- Chinese Academy of Sciences
- Beijing 100190
| | - Cheng-Wen Liu
- Beijing National Laboratory for Molecular Sciences
- Institute of Theoretical and Computational Chemistry
- College of Chemistry and Molecular Engineering
- Peking University
- Beijing 100871
| | - Hong-Guang Xu
- Beijing National Laboratory for Molecular Sciences
- State Key Laboratory of Molecular Reaction Dynamics
- Institute of Chemistry
- Chinese Academy of Sciences
- Beijing 100190
| | - Xiang Zhao
- Institute for Chemical Physics
- School of Science, Xi'an Jiaotong University
- Xi'an 710049
- China
| | - Yi Qin Gao
- Beijing National Laboratory for Molecular Sciences
- Institute of Theoretical and Computational Chemistry
- College of Chemistry and Molecular Engineering
- Peking University
- Beijing 100871
| | - Wei-Jun Zheng
- Beijing National Laboratory for Molecular Sciences
- State Key Laboratory of Molecular Reaction Dynamics
- Institute of Chemistry
- Chinese Academy of Sciences
- Beijing 100190
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8
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Feng G, Hou GL, Xu HG, Zeng Z, Zheng WJ. On the dissolution of lithium sulfate in water: anion photoelectron spectroscopy and density functional theory calculations. Phys Chem Chem Phys 2015; 17:5624-31. [PMID: 25623553 DOI: 10.1039/c4cp05698a] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The initial dissolution steps of lithium sulfate (Li2SO4) in water were investigated by performing anion photoelectron spectroscopy and density functional theory calculations on the Li2SO4(H2O)n(-) (n = 0-5) clusters. The plausible structures of these clusters and the corresponding neutral clusters were obtained using LC-ωPBE/6-311++G(d,p) calculations by comparing the experimental and theoretical vertical electron detachment energies. Two types of structures for bare Li2SO4(-/0) were found: a turtle-shaped structure and a propeller-shaped structure. For Li2SO4(H2O)n(-) cluster anions with n = 1-3, two kinds of isomers derived from the turtle-shaped and propeller-shaped structures of bare Li2SO4(-) were identified. For n = 4-5, these two kinds of isomers present similar structural and energetic features and thus are not distinguishable. For the anionic clusters the water molecules prefer to firstly interact with one Li atom until fully coordinating it. While for the neutral clusters, the water molecules interact with the two Li atoms alternately, therefore, showing a pairwise solvation behavior. The Li-S distance increases smoothly upon addition of water molecules one by one. Addition of five water molecules to Li2SO4 cannot induce the dissociation of one Li(+) ion because the water molecules are shared by two Li(+) ions.
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Affiliation(s)
- Gang Feng
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
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9
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Liu CW, Wang F, Yang L, Li XZ, Zheng WJ, Gao YQ. Stable Salt–Water Cluster Structures Reflect the Delicate Competition between Ion–Water and Water–Water Interactions. J Phys Chem B 2014; 118:743-51. [DOI: 10.1021/jp408439j] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Cheng-Wen Liu
- Institute
of Theoretical and Computational Chemistry, College of Chemistry and
Molecular Engineering, Beijing National Laboratory for Molecular Sciences, Peking University, Beijing 100871, China
| | - Feng Wang
- Department
of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, United States
| | - Lijiang Yang
- Institute
of Theoretical and Computational Chemistry, College of Chemistry and
Molecular Engineering, Beijing National Laboratory for Molecular Sciences, Peking University, Beijing 100871, China
| | - Xin-Zheng Li
- School
of Physics, Peking University, Beijing 100871, China
| | - Wei-Jun Zheng
- Beijing
National Laboratory for Molecular Sciences, State Key Laboratory of
Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Yi Qin Gao
- Institute
of Theoretical and Computational Chemistry, College of Chemistry and
Molecular Engineering, Beijing National Laboratory for Molecular Sciences, Peking University, Beijing 100871, China
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10
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Schmidt TC, Paasche A, Grebner C, Ansorg K, Becker J, Lee W, Engels B. QM/MM investigations of organic chemistry oriented questions. Top Curr Chem (Cham) 2014; 351:25-101. [PMID: 22392477 DOI: 10.1007/128_2011_309] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
About 35 years after its first suggestion, QM/MM became the standard theoretical approach to investigate enzymatic structures and processes. The success is due to the ability of QM/MM to provide an accurate atomistic picture of enzymes and related processes. This picture can even be turned into a movie if nuclei-dynamics is taken into account to describe enzymatic processes. In the field of organic chemistry, QM/MM methods are used to a much lesser extent although almost all relevant processes happen in condensed matter or are influenced by complicated interactions between substrate and catalyst. There is less importance for theoretical organic chemistry since the influence of nonpolar solvents is rather weak and the effect of polar solvents can often be accurately described by continuum approaches. Catalytic processes (homogeneous and heterogeneous) can often be reduced to truncated model systems, which are so small that pure quantum-mechanical approaches can be employed. However, since QM/MM becomes more and more efficient due to the success in software and hardware developments, it is more and more used in theoretical organic chemistry to study effects which result from the molecular nature of the environment. It is shown by many examples discussed in this review that the influence can be tremendous, even for nonpolar reactions. The importance of environmental effects in theoretical spectroscopy was already known. Due to its benefits, QM/MM can be expected to experience ongoing growth for the next decade.In the present chapter we give an overview of QM/MM developments and their importance in theoretical organic chemistry, and review applications which give impressions of the possibilities and the importance of the relevant effects. Since there is already a bunch of excellent reviews dealing with QM/MM, we will discuss fundamental ingredients and developments of QM/MM very briefly with a focus on very recent progress. For the applications we follow a similar strategy.
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Affiliation(s)
- Thomas C Schmidt
- Institut für Phys. und Theor. Chemie, Emil-Fischer-Strasse 42, Campus Hubland Nord, 97074, Würzburg, Germany
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11
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Li RZ, Liu CW, Gao YQ, Jiang H, Xu HG, Zheng WJ. Microsolvation of LiI and CsI in Water: Anion Photoelectron Spectroscopy and ab initio Calculations. J Am Chem Soc 2013; 135:5190-9. [PMID: 23432353 DOI: 10.1021/ja4006942] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ren-Zhong Li
- Beijing National Laboratory
for Molecular Sciences, State Key Laboratory of Molecular Reaction
Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Cheng-Wen Liu
- Beijing National Laboratory
for Molecular Sciences, Institute of Theoretical and Computational
Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Yi Qin Gao
- Beijing National Laboratory
for Molecular Sciences, Institute of Theoretical and Computational
Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Hong Jiang
- Beijing National Laboratory
for Molecular Sciences, Institute of Theoretical and Computational
Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Hong-Guang Xu
- Beijing National Laboratory
for Molecular Sciences, State Key Laboratory of Molecular Reaction
Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Wei-Jun Zheng
- Beijing National Laboratory
for Molecular Sciences, State Key Laboratory of Molecular Reaction
Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
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12
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Koch DM, Peslherbe GH. Importance of polarization in quantum mechanics/molecular mechanics descriptions of electronic excited states: NaI(H2O)n photodissociation dynamics as a case study. J Phys Chem B 2008; 112:636-49. [PMID: 18183959 DOI: 10.1021/jp709656z] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Sodium iodide has long been a paradigm for ionic and covalent curve crossing and ultrafast nonadiabatic dynamics, and our interest lies in the influence of solvation on this process. The NaI(H2O)n photodissociation dynamics are simulated with the molecular dynamics with quantum transitions method. A quantum mechanics/molecular mechanics (QM/MM) description is adopted for the NaI(H2O)n electronic states, in which a semiempirical valence bond approach is used to describe the NaI electronic structure, and a polarizable optimized potential for cluster simulations model is used to describe solute-solvent and solvent-solvent interactions. In contrast to previous work with a nonpolarizable MM model [Koch et al., J. Phys. Chem. A, 2006, 110, 1438], this approach predicts that the NaI ionic ground- to covalent first-excited-state Franck-Condon energy gaps reach a plateau by cluster size 16, in relatively good agreement with experiment and electronic structure calculations; this allows us to safely extend our previous simulations to larger cluster sizes, i.e., n > 4. The simulations suggest that the disappearance of the two-photon ionization probe signals observed in femtosecond pump-probe experiments of NaI(H2O)n, n >/= 4, is due to the shift of the NaI curve-crossing region toward larger NaI internuclear separations because of solvent stabilization of the NaI ionic state. Further, the latter causes the adiabatic ground and excited states to acquire pure ionic and covalent character, respectively, by cluster 8, resulting in NaI ionic ground-state recombination or dissociation. To make a connection with electron transfer in solution, free energy curves have been generated as a function of a solvent coordinate similar to that of solution theory. Inspection of the free energy curves together with the results of excited-state simulations reveal that the electron-transfer process in clusters is not governed by the collective motion of the solvent molecules, as in solution, but that it rather proceeds along the NaI internuclear separation coordinate, as in the gas phase. In fact, solvation in small clusters mainly influences the nonadiabatic dynamics by modulating the NaI internuclear separation at which the ionic and covalent curve-crossing region occurs. Furthermore, the simulations show that electron transfer does not occur in the inverted regime, as predicted by the free energy curves, because of the extreme nonequilibrium nature of the NaI(H2O)n photodissociation process, and the rate of electron transfer increases with cluster size and increasing solvation. Overall, this work demonstrates the importance of including polarization in realistic excited-state simulations of NaI(H2O)n relaxation.
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Affiliation(s)
- Denise M Koch
- Centre for Research in Molecular Modeling (CERMM) and Department of Chemistry and Biochemistry, Concordia University, 7141 Sherbrooke Street West, Montreal (Quebec), Canada
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13
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Nguyen TNV, Hughes SR, Peslherbe GH. Microsolvation of the Sodium and Iodide Ions and Their Ion Pair in Acetonitrile Clusters: A Theoretical Study. J Phys Chem B 2008; 112:621-35. [DOI: 10.1021/jp076567k] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Tao-Nhân V. Nguyen
- Centre for Research in Molecular Modeling and Department of Chemistry & Biochemistry, Concordia University, Montréal, Québec, Canada, H4B 1R6
| | - Sean R. Hughes
- Centre for Research in Molecular Modeling and Department of Chemistry & Biochemistry, Concordia University, Montréal, Québec, Canada, H4B 1R6
| | - Gilles H. Peslherbe
- Centre for Research in Molecular Modeling and Department of Chemistry & Biochemistry, Concordia University, Montréal, Québec, Canada, H4B 1R6
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