We develop a benchmark system for van der Waals interactions obtained with MP2+△CCSD(T)method at complete basis set limit.With this benchmark,we examine the widely used PBE+D3 method and recently developed SCAN+rVV10...We develop a benchmark system for van der Waals interactions obtained with MP2+△CCSD(T)method at complete basis set limit.With this benchmark,we examine the widely used PBE+D3 method and recently developed SCAN+rVV10 method for density functional theory calculations.Our benchmark is based on two molecules:glycine(or Gly,an amino acid)and uracil(or U,an RNA base).We consider six dimer configurations of the two monomers and their potential energy surfaces as a function of relative distance and rotation angle.The Gly-Gly,Gly-U,and U-U pairs represent London dispersion,hydrogen bonding,andπ–πstacking interactions,respectively.Our results show that both PBE+D3 and SCAN+rVV10 methods can yield accuracy better than 1 kcal/mol,except for the cases when the distance between the two monomers is significantly smaller than the equilibrium distance.In such a case,neither of these methods can yield uniformly accurate results for all the configurations.In addition,it is found that the SCAN and SCAN+rVV10 methods can reproduce some subtle features in a rotational potential energy curve,while the PBE,PBE+D3,and the local density approximation fail.展开更多
Two possible reaction mechanisms of VS^＋（^3∑^-, 1^Г） with CO in the gas phase have been studied by using B3LYP/TZVP and CCSD（T）/6-311＋G （3df, 3pd） methods： the O/S exchange reaction （VS^＋＋CO→VO^＋＋CS）...Two possible reaction mechanisms of VS^＋（^3∑^-, 1^Г） with CO in the gas phase have been studied by using B3LYP/TZVP and CCSD（T）/6-311＋G （3df, 3pd） methods： the O/S exchange reaction （VS^＋＋CO→VO^＋＋CS） and the S-transfer reaction （VS^＋ ＋ CO → V^＋ ＋ COS）. The two reactions proceed via two-step and one-step mechanism, respectively. The barriers of the triplet and singlet PESs are 30.6 and 50.9 kcal/mol, respectively, for O/S exchange reaction and 7.3 and 50.2 kcal/mol, respectively, for the S-transfer reaction. The results indicate that the triplet ground state reaction is more favorable, and the S-transfer reaction is more favorable than the O/S exchange reaction, which is in good agreement with the experimental observation.展开更多
Two possible reactions of NbS＋ （3∑^-, 1Г） with CO in the gas phase have been studied by using B3LYP and CCSD（T） methods： the O/S exchange reaction （NbS^＋ ＋ CO → NbO^＋ ＋ CS） and the S-transfer reaction ...Two possible reactions of NbS＋ （3∑^-, 1Г） with CO in the gas phase have been studied by using B3LYP and CCSD（T） methods： the O/S exchange reaction （NbS^＋ ＋ CO → NbO^＋ ＋ CS） and the S-transfer reaction （NbS＋ ＋ CO → Nb^＋ ＋ COS）. The two reactions have a one-step mechanism. The barriers of the O/S exchange reaction on the triplet and singlet surfaces are 51.2 and 52.4 kcal/mol, respectively, and the barriers of the S-transfer reaction are 58.3 and 78.0 kcal/mol, respectively. The results indicate that the Stransfer and the O/S exchange reaction of the 3∑^- ground state of NbS＋ are competing, but, for the S-transfer reaction, the 1F exited state is more reactive. The differences between the reactions of NbS＋ （3∑^_, 1Г） and VS＋ （3∑^_, 1Г） are discussed.展开更多
The reactions of Mn＋（7S,5S） with CS2 have been studied at the B3LYP/TZVP level on both septuplet and quintet potential energy surfaces（PESs）.The overall energies have been refined at the CCSD（T） level.The calcu...The reactions of Mn＋（7S,5S） with CS2 have been studied at the B3LYP/TZVP level on both septuplet and quintet potential energy surfaces（PESs）.The overall energies have been refined at the CCSD（T） level.The calculated results indicate that the reactions of Mn＋（7S,5S） with CS2 proceed via an insertion-elimination mechanism.Calculations show that the quintet reaction is more favorable than the septuplet under high energy conditions.The spin-forbidden reaction Mn＋（7S） ＋ CS2 → MnS＋（5Π） ＋ CS proceeds through a septuplet-quintet surface and the crossing seam is approximately determined.All results have been compared with the existing experimental and theoretical data.展开更多
The accurate equilibrium structures of S_3 and S_3^- are determined by the coupled-cluster method with single, double excitation and perturbative triple excitation(CCSD(T)) with basis sets of aug-cc-pV(n+d)Z(n = T, Q,...The accurate equilibrium structures of S_3 and S_3^- are determined by the coupled-cluster method with single, double excitation and perturbative triple excitation(CCSD(T)) with basis sets of aug-cc-pV(n+d)Z(n = T, Q, 5, or 6), complete basis set extrapolation functions with two-parameters and three-parameters, together with considering the contributions due to the core-valence electron correlation, scalar relativistic effects, spin–orbit coupling, and zero-point vibrational corrections. Our calculations show that both the neutral S_3 and anion S_3^- have open forms with C_(2r) vsymmetry. On the basis of the stable geometries, the adiabatic electron affinity of S_3 is determined to be 19041(11) cm^(-1), which is in excellent agreement with the experimental data(19059(7) cm^(-1)). The dependence of geometries and electron affinity on the computation level and physical corrections is discussed. The present computational results are helpful to the experimental molecular spectroscopy and bonding of S_3.展开更多
Ab initio study of the equilibrium structure, spectroscopy constants, and anharmonic force field for several isotopomers of germanium dichloride （70GeCl2, 72GECl2, and 76GeCl2） have been carried out at the MP2 and C...Ab initio study of the equilibrium structure, spectroscopy constants, and anharmonic force field for several isotopomers of germanium dichloride （70GeCl2, 72GECl2, and 76GeCl2） have been carried out at the MP2 and CCSD（T） levels of theory using cc-pVTZ basis set. The cal- culated geometries, rotational constants, vibration-rotation interaction constants, harmonic frequencies, anharmonic constants, quartic and sextic centrifugal distortion constants, cubic and quartic force constants are compared with experimental data. For small mass differences of the Ge isotopes, the isotopic effects for germanium dichloride are much weaker. The agreements are satisfactory for these two methods, but the deviations of CCSD（T） results are slightly larger than that of MP2, because of CCSD（T）＇s inadequate treatment of electron correlation in hypervalent Cl atom.展开更多
To elucidate the mechanisms of Zr ＋ reacting with COS,both the quartet and doublet potential energy surfaces （PESs） for reactions of Zr ＋ （4 F,2 D） with COS in the gas phase have been investigated in detail by m...To elucidate the mechanisms of Zr ＋ reacting with COS,both the quartet and doublet potential energy surfaces （PESs） for reactions of Zr ＋ （4 F,2 D） with COS in the gas phase have been investigated in detail by means of density functional method （B3LYP）.To obtain more accurate results,the coupled cluster single-point calculations （CCSD（T）） using B3LYP optimized geometries were performed.For the C-O bond activation,the calculated results indicate that both the quartet and doublet states proceed via an insertion-elimination mechanism.For the C-S bond activation,the quartet reaction has an insertion-elimination mechanism,but the doublet reaction is a direct abstraction of the sulfur atom by Zr ＋.The C-S bond activation is found to be energetically more favorable than the C-O bond activation.It is found that the reaction of the 4 F gound state of Zr ＋ to yield ZrO ＋ is spin-forbidden （Zr ＋ （4 F） ＋ COS （1 Σ） → ZrO ＋ （2） ＋ CS （1 Σ）） and the crossing points were approximately determined.All the results have been compared with the existing experimental and theoretical data.展开更多
The reaction mechanism of photochemical reaction between Br2 (1Σ ) and OCS (1Σ ) is predicted by means of theoretical methods. The calculated results indicate that the direct addition of Br2 to the CS bond of OCS ...The reaction mechanism of photochemical reaction between Br2 (1Σ ) and OCS (1Σ ) is predicted by means of theoretical methods. The calculated results indicate that the direct addition of Br2 to the CS bond of OCS molecule is more favorable in energy than the direct addition of Br2 to the CO bond. Furthermore, the intermediate isomer syn-BrC(O)SBr is more stable thermodynamically and kinetically than anti-BrC(O)SBr. The original resultant anti-BrC(O)SBr formed in the most favorable reaction channel can easily isomerize into the final product syn-BrC(O)SBr with only 31.72 kJ/mol reaction barrier height. The suggested mechanism is in good agreement with previous experimental study.展开更多
Recently,AnstÖter and co-workers[J.Am.Chem.Soc.141,6132(2019)]have provided the first photoelectron spectroscopic determination of the anion-πbond strength(De)using iodide-hexafluorobenzene(I-·C6F6)as the a...Recently,AnstÖter and co-workers[J.Am.Chem.Soc.141,6132(2019)]have provided the first photoelectron spectroscopic determination of the anion-πbond strength(De)using iodide-hexafluorobenzene(I-·C6F6)as the archetypical system.In combination with an equation-of-motion coupled cluster theory,namely EOM-IP-CCSD(d T),using Dunning’s aug-cc-p VDZ(a VDZ)basis set,Dein I-·C6F6 was found to be-0.53 e V with an uncertainty less than±0.03 e V.The interaction was claimed to arise for a large part from correlation forces(41%)with only a 23%contribution from electrostatic forces.In the present work,we performed the coupled-cluster with single and double and perturbative triple excitations,CCSD(T),calculations.We found that CCSD(T)/a VDZ can have an uncertainty up to 0.113 e V due to the basis set incompleteness.Our calculations disclosed that the previous calculations on the electrostatic contribution are concealed by the contributions from the exchange and Pauli repulsion.The electrostatic contribution is actually determinant,being more than double of the correlation contribution in the I-·C6F6 complex at the equilibrium binding distance.展开更多
The effects of low-level PES on the overall accuracy of the final surface constructed by using hierarchical construction were investigated with the constructions of a number of global surfaces for the H3 system at UHF...The effects of low-level PES on the overall accuracy of the final surface constructed by using hierarchical construction were investigated with the constructions of a number of global surfaces for the H3 system at UHF （UMP2, DFT-B3LYP, UCCSD（T））/vtz, and UCCSD（T）/avqz levels of theory. The total reaction probabilities for the H＋H2 reaction calculated on these surfaces revealed that the accuracy of UCCSD（T）/avqz surface is very close to the well-known BKMP2 surface, while the UCCSD（T）/vtz PES has a slightly higher barrier. In contrast, the low-level theories （UHF, UMP2, DFT-B3LYP） with vtz basis set can only provide a qualitative description of this simplest reaction despite the fact that they are widely used to study reactions in complex systems. On the other hand, although these theories are not accurate on describing the reaction, they can be used to provide the low- level PESs for hierarchical construction of the UCCSD（T）/avqz PES with the number of UCCSD（T）/avqz energies substantially reduced.展开更多
We present a theoretical study of the reaction of the hydroxyl radical with ethene using electronic structure calculations and direct-dynamics simulations. High-accuracy electronic structure calculations at the CCSD（...We present a theoretical study of the reaction of the hydroxyl radical with ethene using electronic structure calculations and direct-dynamics simulations. High-accuracy electronic structure calculations at the CCSD（T）/aug-cc-pVTZ//MP2/aug-ce-pVDZ level have been carried out to characterize the representative regions of the potential energy surface of various reaction pathways, including OH-addition and H-abstraction. These ab initio calculations have been employed to derive an improved set of parameters for the MSINDO semiempirieal Hamiltonian specific to the OH＋C2H4 reaction. The specific-reaction-parameter Hamilto- nian captures the ab initio data accurately, and has been used to perform direct quasiclassica] trajectory simulations of the OH＋C2H4 reaction at collision energies in the range of 2-10 kcal/mol. The calculated cross sections reveal that the OH-addition reaction domi- nates at all energies over H-abstraction. In addition, the excitation function of addition is reminiscent of a barrierless capture process, while that for abstraction corresponds to an activated one, and these trends can be connected to the transition-state energies of both reactions. We note that the development of an accurate semiempirical Hamiltonian for the OH＋C2H4 reaction in this work required the inclusion of empirical dispersion corrections, which will be important in future applications for which long-range intermoleeular attraction becomes significant.展开更多
The C-I bond dissociation enthalpies （BDE） of various organic iodides were calculated using high-level theoretical methods including MP2 and CCSD（T） with extrapolated basis set as well as a number of density funct...The C-I bond dissociation enthalpies （BDE） of various organic iodides were calculated using high-level theoretical methods including MP2 and CCSD（T） with extrapolated basis set as well as a number of density functional theory methods. After systematic evaluation of the theoretical results against available experimental C-I BDEs, it was found that the MPW LYPIM method gave the lowest root mean square error. We, therefore, used this method to examine the substituent effects on different categories of C（sp3）-I and C（sp2）-I bonds. Fur thermore, the remote substituent effects on the C-I BDEs of substituted iodobenzenes and substituted （iodomethyl）benzenes were also investigated at the same level. The C-I BDEs of typical heteroaromatic iodides including five-membered and six-membered heterocyclic iodides were also examined.展开更多
基金supported by US National Science Foundation under Grant No. DMREF-1627028
文摘We develop a benchmark system for van der Waals interactions obtained with MP2+△CCSD(T)method at complete basis set limit.With this benchmark,we examine the widely used PBE+D3 method and recently developed SCAN+rVV10 method for density functional theory calculations.Our benchmark is based on two molecules:glycine(or Gly,an amino acid)and uracil(or U,an RNA base).We consider six dimer configurations of the two monomers and their potential energy surfaces as a function of relative distance and rotation angle.The Gly-Gly,Gly-U,and U-U pairs represent London dispersion,hydrogen bonding,andπ–πstacking interactions,respectively.Our results show that both PBE+D3 and SCAN+rVV10 methods can yield accuracy better than 1 kcal/mol,except for the cases when the distance between the two monomers is significantly smaller than the equilibrium distance.In such a case,neither of these methods can yield uniformly accurate results for all the configurations.In addition,it is found that the SCAN and SCAN+rVV10 methods can reproduce some subtle features in a rotational potential energy curve,while the PBE,PBE+D3,and the local density approximation fail.
基金the National Natural Science Foundation of China(No.20563005)the High Performance Computer Center of Yunnan University.
文摘Two possible reaction mechanisms of VS^＋（^3∑^-, 1^Г） with CO in the gas phase have been studied by using B3LYP/TZVP and CCSD（T）/6-311＋G （3df, 3pd） methods： the O/S exchange reaction （VS^＋＋CO→VO^＋＋CS） and the S-transfer reaction （VS^＋ ＋ CO → V^＋ ＋ COS）. The two reactions proceed via two-step and one-step mechanism, respectively. The barriers of the triplet and singlet PESs are 30.6 and 50.9 kcal/mol, respectively, for O/S exchange reaction and 7.3 and 50.2 kcal/mol, respectively, for the S-transfer reaction. The results indicate that the triplet ground state reaction is more favorable, and the S-transfer reaction is more favorable than the O/S exchange reaction, which is in good agreement with the experimental observation.
基金supported by the National Natural Science Foundation of China(No.20563005)the Key Laboratory of Forest Resources Conservation and Use in the Southwest Mountains of China(Southwest Forestry University)the General Program of the Applied Basic Research of Science and Technology Department of Yunnan Province
文摘Two possible reactions of NbS＋ （3∑^-, 1Г） with CO in the gas phase have been studied by using B3LYP and CCSD（T） methods： the O/S exchange reaction （NbS^＋ ＋ CO → NbO^＋ ＋ CS） and the S-transfer reaction （NbS＋ ＋ CO → Nb^＋ ＋ COS）. The two reactions have a one-step mechanism. The barriers of the O/S exchange reaction on the triplet and singlet surfaces are 51.2 and 52.4 kcal/mol, respectively, and the barriers of the S-transfer reaction are 58.3 and 78.0 kcal/mol, respectively. The results indicate that the Stransfer and the O/S exchange reaction of the 3∑^- ground state of NbS＋ are competing, but, for the S-transfer reaction, the 1F exited state is more reactive. The differences between the reactions of NbS＋ （3∑^_, 1Г） and VS＋ （3∑^_, 1Г） are discussed.
基金Suppoted by the Science Foundation of Qujing Normal School (No2008QN004)the Scientific Research Fund of Yunnan Provincial Education Department (No 08Y0195)the Scientific Research Fund of Yunnan Provincial Education Department (No 09C0187)
文摘The reactions of Mn＋（7S,5S） with CS2 have been studied at the B3LYP/TZVP level on both septuplet and quintet potential energy surfaces（PESs）.The overall energies have been refined at the CCSD（T） level.The calculated results indicate that the reactions of Mn＋（7S,5S） with CS2 proceed via an insertion-elimination mechanism.Calculations show that the quintet reaction is more favorable than the septuplet under high energy conditions.The spin-forbidden reaction Mn＋（7S） ＋ CS2 → MnS＋（5Π） ＋ CS proceeds through a septuplet-quintet surface and the crossing seam is approximately determined.All results have been compared with the existing experimental and theoretical data.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11874179,11447194,11574114,and 11874177)the Natural Science Foundation of Jilin Province,China(Grant No.20180101289JC)
文摘The accurate equilibrium structures of S_3 and S_3^- are determined by the coupled-cluster method with single, double excitation and perturbative triple excitation(CCSD(T)) with basis sets of aug-cc-pV(n+d)Z(n = T, Q, 5, or 6), complete basis set extrapolation functions with two-parameters and three-parameters, together with considering the contributions due to the core-valence electron correlation, scalar relativistic effects, spin–orbit coupling, and zero-point vibrational corrections. Our calculations show that both the neutral S_3 and anion S_3^- have open forms with C_(2r) vsymmetry. On the basis of the stable geometries, the adiabatic electron affinity of S_3 is determined to be 19041(11) cm^(-1), which is in excellent agreement with the experimental data(19059(7) cm^(-1)). The dependence of geometries and electron affinity on the computation level and physical corrections is discussed. The present computational results are helpful to the experimental molecular spectroscopy and bonding of S_3.
文摘Ab initio study of the equilibrium structure, spectroscopy constants, and anharmonic force field for several isotopomers of germanium dichloride （70GeCl2, 72GECl2, and 76GeCl2） have been carried out at the MP2 and CCSD（T） levels of theory using cc-pVTZ basis set. The cal- culated geometries, rotational constants, vibration-rotation interaction constants, harmonic frequencies, anharmonic constants, quartic and sextic centrifugal distortion constants, cubic and quartic force constants are compared with experimental data. For small mass differences of the Ge isotopes, the isotopic effects for germanium dichloride are much weaker. The agreements are satisfactory for these two methods, but the deviations of CCSD（T） results are slightly larger than that of MP2, because of CCSD（T）＇s inadequate treatment of electron correlation in hypervalent Cl atom.
基金Suppoted by the Science Foundation of Qujing Normal School (No. 2008QN004)the Scientific Research Fund of Yunnan Provincial Education (No. 09C0187)the Scientific Research Fund of Yunnan Provincial Education (No. 09Y0392)
文摘To elucidate the mechanisms of Zr ＋ reacting with COS,both the quartet and doublet potential energy surfaces （PESs） for reactions of Zr ＋ （4 F,2 D） with COS in the gas phase have been investigated in detail by means of density functional method （B3LYP）.To obtain more accurate results,the coupled cluster single-point calculations （CCSD（T）） using B3LYP optimized geometries were performed.For the C-O bond activation,the calculated results indicate that both the quartet and doublet states proceed via an insertion-elimination mechanism.For the C-S bond activation,the quartet reaction has an insertion-elimination mechanism,but the doublet reaction is a direct abstraction of the sulfur atom by Zr ＋.The C-S bond activation is found to be energetically more favorable than the C-O bond activation.It is found that the reaction of the 4 F gound state of Zr ＋ to yield ZrO ＋ is spin-forbidden （Zr ＋ （4 F） ＋ COS （1 Σ） → ZrO ＋ （2） ＋ CS （1 Σ）） and the crossing points were approximately determined.All the results have been compared with the existing experimental and theoretical data.
基金supported by the National Namral Science Foundation of China(Nos.20301006,20271019)the Doctoral Foundation of Heilongjiang University(2002).
文摘The reaction mechanism of photochemical reaction between Br2 (1Σ ) and OCS (1Σ ) is predicted by means of theoretical methods. The calculated results indicate that the direct addition of Br2 to the CS bond of OCS molecule is more favorable in energy than the direct addition of Br2 to the CO bond. Furthermore, the intermediate isomer syn-BrC(O)SBr is more stable thermodynamically and kinetically than anti-BrC(O)SBr. The original resultant anti-BrC(O)SBr formed in the most favorable reaction channel can easily isomerize into the final product syn-BrC(O)SBr with only 31.72 kJ/mol reaction barrier height. The suggested mechanism is in good agreement with previous experimental study.
基金supported by the National Natural Science Foundation of China(No.21688102 and No.91027044)。
文摘Recently,AnstÖter and co-workers[J.Am.Chem.Soc.141,6132(2019)]have provided the first photoelectron spectroscopic determination of the anion-πbond strength(De)using iodide-hexafluorobenzene(I-·C6F6)as the archetypical system.In combination with an equation-of-motion coupled cluster theory,namely EOM-IP-CCSD(d T),using Dunning’s aug-cc-p VDZ(a VDZ)basis set,Dein I-·C6F6 was found to be-0.53 e V with an uncertainty less than±0.03 e V.The interaction was claimed to arise for a large part from correlation forces(41%)with only a 23%contribution from electrostatic forces.In the present work,we performed the coupled-cluster with single and double and perturbative triple excitations,CCSD(T),calculations.We found that CCSD(T)/a VDZ can have an uncertainty up to 0.113 e V due to the basis set incompleteness.Our calculations disclosed that the previous calculations on the electrostatic contribution are concealed by the contributions from the exchange and Pauli repulsion.The electrostatic contribution is actually determinant,being more than double of the correlation contribution in the I-·C6F6 complex at the equilibrium binding distance.
文摘The effects of low-level PES on the overall accuracy of the final surface constructed by using hierarchical construction were investigated with the constructions of a number of global surfaces for the H3 system at UHF （UMP2, DFT-B3LYP, UCCSD（T））/vtz, and UCCSD（T）/avqz levels of theory. The total reaction probabilities for the H＋H2 reaction calculated on these surfaces revealed that the accuracy of UCCSD（T）/avqz surface is very close to the well-known BKMP2 surface, while the UCCSD（T）/vtz PES has a slightly higher barrier. In contrast, the low-level theories （UHF, UMP2, DFT-B3LYP） with vtz basis set can only provide a qualitative description of this simplest reaction despite the fact that they are widely used to study reactions in complex systems. On the other hand, although these theories are not accurate on describing the reaction, they can be used to provide the low- level PESs for hierarchical construction of the UCCSD（T）/avqz PES with the number of UCCSD（T）/avqz energies substantially reduced.
文摘We present a theoretical study of the reaction of the hydroxyl radical with ethene using electronic structure calculations and direct-dynamics simulations. High-accuracy electronic structure calculations at the CCSD（T）/aug-cc-pVTZ//MP2/aug-ce-pVDZ level have been carried out to characterize the representative regions of the potential energy surface of various reaction pathways, including OH-addition and H-abstraction. These ab initio calculations have been employed to derive an improved set of parameters for the MSINDO semiempirieal Hamiltonian specific to the OH＋C2H4 reaction. The specific-reaction-parameter Hamilto- nian captures the ab initio data accurately, and has been used to perform direct quasiclassica] trajectory simulations of the OH＋C2H4 reaction at collision energies in the range of 2-10 kcal/mol. The calculated cross sections reveal that the OH-addition reaction domi- nates at all energies over H-abstraction. In addition, the excitation function of addition is reminiscent of a barrierless capture process, while that for abstraction corresponds to an activated one, and these trends can be connected to the transition-state energies of both reactions. We note that the development of an accurate semiempirical Hamiltonian for the OH＋C2H4 reaction in this work required the inclusion of empirical dispersion corrections, which will be important in future applications for which long-range intermoleeular attraction becomes significant.
文摘The C-I bond dissociation enthalpies （BDE） of various organic iodides were calculated using high-level theoretical methods including MP2 and CCSD（T） with extrapolated basis set as well as a number of density functional theory methods. After systematic evaluation of the theoretical results against available experimental C-I BDEs, it was found that the MPW LYPIM method gave the lowest root mean square error. We, therefore, used this method to examine the substituent effects on different categories of C（sp3）-I and C（sp2）-I bonds. Fur thermore, the remote substituent effects on the C-I BDEs of substituted iodobenzenes and substituted （iodomethyl）benzenes were also investigated at the same level. The C-I BDEs of typical heteroaromatic iodides including five-membered and six-membered heterocyclic iodides were also examined.
