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1.
This study revisits the stability of the possible conformations and the decomposition reactions of ethyl formate in the S0 state using the (U)MP2, MP4SDTQ, CCSD(T), and (U)B3LYP methods with various basis sets. The transition states of the decomposition channels to HCOOH + C2H4, CO + CH3CH2OH, CH2O + CH3CHO, HCOH + CH3CHO, C2H6 + CO2, and H2 + CH2CHOCHO are determined. The microcanonical rate constants derived from the RRKM theory are calculated for each of the decomposition reactions. The high‐pressure limit rate constants are calculated for the decomposition channels to HCOOH + C2H4, CO + CH3CH2OH, and CH2O + CH3CHO.  相似文献   

2.
A new non-symmetric N(OH)3 species more stable than the C3 structure is found at Density Functional Theory (B3PW91, B3LYP), MP2, MP4 and CCSD(T) levels with extended basis sets. C1 and C3 structures are qualitatively different from those of the As(OH)3 molecule. Energy differences and interconversion barriers become smaller with increasing inclusion of electronic correlation. However at the MP2, MP4 and CCSD(T) levels, these differences increase with basis set quality. ZPE corrections lead to barrier collapse but only at the CCSD(T)/AVTZ level. The C1 and C3 MP2/AVTZ infrared spectra are given for future studies.  相似文献   

3.
4.
The accuracy of various computational methods (Hartree–Fock, MP2, CCSD, CAS-SCF, and several types of DFT) for predicting relative intensities in Raman spectra for C6H6, C6D6, and C6F6 was compared. The predicted relative intensities for ν1 and ν2 were compared with relative intensities measured by an FT-Raman spectrometer. While none of these methods excelled at this prediction, Hartree–Fock with a large basis set was most successful for C6H6 and C6D6, while PW91PW91 was the most successful for C6F6.  相似文献   

5.
The potential of nuclear magnetic resonance (NMR) technique in probing the structure of porous systems including carbon nanostructures filled with inert gases is analysed theoretically using accurate calculations of neon (21Ne) nuclear magnetic shieldings. The CBS estimates of 21Ne NMR parameters were performed for single atom, its dimer and neon interacting with acetylene, ethylene and 1,3‐cyclopentadiene. Several levels of theory including restricted Hartree‐Fock (RHF), Møller‐Plesset perturbation theory to the second order (MP2), density functional theory (DFT) with van Voorhis and Scuseria's t‐dependent gradient‐corrected correlation functional (VSXC), coupled cluster with single and doubles excitations (CCSD), with single, doubles and triples included in a perturbative way (CCSD(T)) and single, doubles and tripes excitations (CCSDT) combined with polarization‐consistent aug‐pcS‐n series of basis sets were employed. The impact of neon confinement inside selected fullerene cages used as an NMR probe was studied at the RHF/pcS‐2 level of theory. A sensitivity of neon probe to the proximity of multiple CC bonds in C2H2, C2H4, C5H6 and inside C28, C30, C32, C34 and C60 fullerenes was predicted from 21Ne NMR parameters' changes. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

6.
Metal atoms were deposited on an Si (111)-7 × 7 surface, and they were adsorbed with alcohol gases (CH3OH/C2H5OH/C3H7OH). Initially, CnH2n+1OH adsorption was simply used as an intermediate layer to prevent the chemical reaction between metal and Si atoms. Through scanning tunneling microscopy (STM) and a mass spectrometer, the CnH2n+1OH dissociation process is further derived as the construction of a surface quasi-potential with horizontal and vertical directions. With the help of three typical metal depositions, the surface characteristics of CH3OH adsorption are more clearly presented in this paper. Adjusting the preheating temperature, the difference of thermal stability between CH3O and H+ could be obviously derived in Au deposition. After a large amount of H+ was separated, the isolation characteristic of CH3O was discussed in the case of Fe deposition. In the process of building a new metal-CH3O-H+ model, the dual characteristics of CH3OH were synthetically verified in Sn deposition. CH3O adsorption is prone to influencing the interaction between the metal deposition and substrate surface in the vertical direction, while H+ adsorption determines the horizontal behavior of metal atoms. These investigations lead one to believe that, to a certain extent, the formation of regular metal atomic structures on the Si (111)-7 × 7-CH3OH surface is promoted, especially according to the dual characteristics and adsorption models we explored.  相似文献   

7.
We present a systematic comparison of the correlation contribution at the level of the second-order polarization propagator approximation (SOPPA ) and MP 2 to the static dipole polarizability of (1) Be, BeH?, BH, CH+, MgH?, AIH, SiH+, and GeH+; (2) BH3, CH4, NH3, H2O, HF, BF, and F2; and (3) N2, CO, CN?, HCN, C2H2, and HCHO . Fairly extended basis sets were used in the calculations. We find that the agreement with experimental values is improved in SOPPA and MP .2 over the results at the SCF level. The signs and magnitudes of the correlation contribution in SOPPA are similar to those obtained in analytical derivative MP 2 calculations. However, it is not possible to say, in general, which method gives the largest correlation contribution or the best agreement with experiment, nor is it possible to make a priori prediction of the sign of the correlation contribution. For the first group of molecules, which have a quasi-degenerate ground state, additional CCDPPA and CCSDPPA calculations were performed and compared with polarizabilities obtained as analytical/numerical derivatives of the CCD and CCSD energies. The CCSDPPA results were found to be in better agreement with other calculations than were the SOPPA results, demonstrating the necessity of using methods based on infinite-order perturbation theory for these systems. © 1994 John Wiley & Sons, Inc.  相似文献   

8.
A series of new Cu(II) complexes with important physiologically active cycloalkane-5-spirohydantoines are synthesized reacting as a result of CuCl2 · 2H2O interaction with the ligands in alkaline water medium. Their structures were studied using spectroscopic (IR and EPR) methods. For comparison, ab initio calculations of the structure and IR spectra of the corresponding Cu(II) complexes were also performed. It was proven that with cyclopentane-5-spirohydantoins, distorted (flattened) tetrahedral structure is realized Cu(L–H)2(H2O)2, while with the higher cycloalkane-5-spirohydantoins linear Cu(II) complexes of the type CuL–H(OH) are formed.  相似文献   

9.
We explored the interactions of gas molecules such as H2, CH4, C2H4, C2H6, CO2, and CS2 sandwiched by two pyrazine (Pz) molecules, which were employed as a model of organic linker in the Hofmann-type metal?Corganic framework (MOF). The MP2.5/aug-cc-pVTZ method was employed here, because this method presents almost the same binding energy as that calculated by the CCSD(T)/aug-cc-pVDZ with MP2.5-evaluated basis set extension effects to aug-cc-pVTZ basis set. The binding energy of the gas molecule increases in the order H2?<?CH4?<?CO2?<?C2H4????C2H6?<?CS2. The energy decomposition analysis of the interaction energy indicates that the electrostatic term presents the largest contribution to the interaction energy at the Hartree?CFock level. However, the dispersion interaction provides dominant contribution to the total binding energy at correlated level. We newly found a linear correlation between the z-component of polarizability of gas molecules and dispersion energy, where the z-axis was taken to be perpendicular to two Pz rings. These results are useful for understanding and predicting the binding energy of the gas molecule with the organic linkers of MOF.  相似文献   

10.
This work characterizes eight stationary points of the P2 dimer and six stationary points of the PCCP dimer, including a newly identified minimum on both potential energy surfaces. Full geometry optimizations and corresponding harmonic vibrational frequencies were computed with the second‐order Møller–Plesset (MP2) electronic structure method and six different basis sets: aug‐cc‐pVXZ, aug‐cc‐pV(X+d)Z, and aug‐cc‐pCVXZ where X = T, Q. A new L‐shaped structure with C2 symmetry is the only minimum for the P2 dimer at the MP2 level of theory with these basis sets. The previously reported parallel‐slipped structure with C2h symmetry and a newly identified cross configuration with D2 symmetry are the only minima for the PCCP dimer. Single point energies were also computed using the canonical MP2 and CCSD(T) methods as well as the explicitly correlated MP2‐F12 and CCSD(T)‐F12 methods and the aug‐cc‐pVXZ (X = D, T, Q, 5) basis sets. The energetics obtained with the explicitly correlated methods were very similar to the canonical results for the larger basis sets. Extrapolations were performed to estimate the complete basis set (CBS) limit MP2 and CCSD(T) binding energies. MP2 and MP2‐F12 significantly overbind the P2 and PCCP dimers relative to the CCSD(T) and CCSD(T)‐F12 binding energies by as much as 1.5 kcal mol?1 for the former and 5.0 kcal mol?1 for the latter at the CBS limit. The dominant attractive component of the interaction energy for each dimer configuration was dispersion according to several symmetry‐adapted perturbation theory analyses. © 2014 Wiley Periodicals, Inc.  相似文献   

11.
The study presents a quantitative estimation of B-Hb⋯π interaction in diborane-localized-π half sandwiches and sandwiches. DFT-D3 method is used for geometry optimization and estimating the stability of the complexes (in terms of stabilization energies). The diborane molecule is the source of bridging hydrogen and O2, C2H4, and C2H2 molecules are considered as the localized π-systems. MP2 and CCSD(T) calculations are also performed to measure the stability of the chosen complexes. Results indicate that the complexes are feebly stable in gas phase with stabilization energies <5.0 kcal mol−1. Compared to DFT-D3 functionals, MP2 calculations are found to be more suitable in predicting the stability of the complexes. Dispersive interaction is the primary mode of interaction in stabilizing the complexes. Presence of substituents either on diborane or on the considered π-systems play key role in stabilizing the complexes. Thermochemical analysis demonstrates the exothermic nature of complexation. 1H and 13B NMR analysis are also performed.  相似文献   

12.
The π–π interactions between CO2 and three aromatic molecules, namely benzene (C6H6), pyridine (C5H5N), and pyrrole (C4H5N), which represent common functional groups in metal‐organic/zeoliticimidazolate framework materials, were characterized using high‐level ab initio methods. The coupled‐cluster with single and double excitations and perturbative treatment of triple excitations (CCSD(T)) method with a complete basis set (CBS) was used to calibrate Hartree–Fock, density functional theory, and second‐order M?ller–Plesset (MP2) with resolution of the identity approximation calculations. Results at the MP2/def2‐QZVPP level showed the smallest deviations (only about 1 kJ/mol) compared with those at the CCSD(T)/CBS level of theory. The strength of π–π binding energies (BEs) followed the order C4H5N > C6H6 ~ C5H5N and was roughly correlated with the aromaticity and the charge transfer between CO2 and aromatic molecule in clusters. Compared with hydrogen‐bond or electron donor–acceptor interactions observed during BE calculations at the MP2/def2‐QZVPP level of theory, π–π interactions significantly contribute to the total interactions between CO2 and aromatic molecules. © 2013 Wiley Periodicals, Inc.  相似文献   

13.
A linear correlation between isotropic nuclear magnetic shielding constants for seven model molecules (CH2O, H2O, HF, F2, HCN, SiH4 and H2S) calculated with 37 methods (34 density functionals, RHF, MP2 and CCSD(T)), with affordable pcS‐2 basis set and corresponding complete basis set results, estimated from calculations with the family of polarization‐consistent pcS‐n basis sets is reported. This dependence was also supported by inspection of profiles of deviation between CBS estimated nuclear shieldings and shieldings obtained with the significantly smaller basis sets pcS‐2 and aug‐cc‐pVTZ‐J for the selected set of 37 calculation methods. It was possible to formulate a practical approach of estimating the values of isotropic nuclear magnetic shielding constants at the CCSD(T)/CBS and MP2/CBS levels from affordable CCSD(T)/pcS‐2, MP2/pcS‐2 and DFT/CBS calculations with pcS‐n basis sets. The proposed method leads to a fairly accurate estimation of nuclear magnetic shieldings and considerable saving of computational efforts. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

14.
Two alternative dehydration reactions C(OH)4 → (HO)2CO + H2O and C(OH)4 + H2O → (HO)2CO + 2H2O are studied by ab initio Becke3LYP/6–311 + G** and MP2/6–31G** methods. Calculated energy and geometry characteristics of intermediates and transition states predict a catalytic effect of one water molecule and the exothermism of the transformations. Relevant HF/6–311 + G**, HF/6–31G**, HF/6–31G, and HF/3–21G calculations were performed for comparison. © 1997 John Wiley & Sons, Inc.  相似文献   

15.
The X(C,N,O)—NO2 bond dissociation energy (BDE) for CH3NO2, C2H3NO2, C2H5NO2, HONO2, CH3ONO2, C2H5ONO2, NH2NO2, (CH3)2NNO2 are computed using the DFT (B3LYP, B3PW91), the single and double-coupled cluster excited (CCSD), and the complete basis set (CBS-Q) methods, with the 6-311G** and cc-pVDZ basis sets. By comparing the computed energies and experimental results, we find that the DFT method can not give good results of BDE, but, the BDEs generated by the CCSD/cc-pVDZ, CBS-Q are in good agreement with experimental values.  相似文献   

16.
The kinetics of the hydrogen abstraction from H2O2 by ?OH has been modeled with MP2/6‐31G*//MP2/6‐31G*, MP2‐SAC//MP2/6‐31G*, MP2/6‐31+G**//MP2/6‐31+G**, MP2‐SAC// MP2/6‐31+G**, MP4(SDTQ)/6‐311G**//MP2/6‐31G*, CCSD(T)/6‐31G*//CCSD(T)/6‐31G*, CCSD(T)/6‐31G**//CCSD(T)/6‐31G**, CCSD(T)/6‐311++G**//MP2/6‐31G* in the gas phase. MD simulations have been used to generate initial geometries for the stationary points along the potential energy surface for hydrogen abstraction from H2O2. The effective fragment potential (EFP) has been used to optimize the relevant structures in solution. Furthermore, the IEFPCM model has been used for the supermolecules generated via MD calculations. IEFPCM/MP2/6‐31G* and IEFPCM/CCSD(T)/6‐31G* calculations have also been performed for structures without explicit water molecules. Experimentally, the rate constant for hydrogen abstraction by ?OH drops from 1.75 × 10?12 cm3 molecule?1 s?1 in the gas phase to 4.48 × 10?14 cm3 molecule?1 s?1 in solution. The same trend has been reproduced best with MP4 (SDTQ)/6‐311G**//MP2/6‐31G* in the gas phase (0.415 × 10?12 cm3 molecule?1 s?1) and with EFP (UHF/6‐31G*) in solution (3.23 × 10?14 cm3 molecule?1 s?1). © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 502–514, 2005  相似文献   

17.
A hybrid method is applied that combines second order Møller–Plesset perturbation theory (MP2) for cluster models with density functional theory for periodic (slab) models to obtain structures and energies for methane and ethane molecules adsorbed on the MgO(001) surface. Single point calculations are performed to estimate the effect of increasing the cluster size on the MP2 energies and to evaluate the difference between coupled cluster (CCSD(T)) and MP2 energies. The final estimates of the adsorption energies are 12.9 ± 1.3 and 18.9 ± 1.8 kJ/mol for CH4 and C2H6, respectively. © 2016 Wiley Periodicals, Inc.  相似文献   

18.
In order to demonstrate the role of the fluorination and some solvents in the structural organization of the Ag(I) coordination polymers with β-diketonate ligands (R1C(O)CαHC(O)R2) we synthesized a series of the compounds containing tfac- (R1 = CH3, R2 = CF3) and pfpac- (R1 = CH3, R2 = C2F5) anions. Solvent-free [Ag(L)] (L = tfac 1, pfpac 2) compounds and the corresponding acetonitrile and toluene adducts have been characterized by elemental analysis and/or NMR, IR and single-crystal XRD. This series includes five new coordination polymers. Compound 1 is a 3D coordination framework based on Ag–Ochelate/bridge, Ag–Cα bonds, and argentophilic interactions. An increase in the fluorinated group leads to a chain coordination polymer 2 of an unusual structural organization. These chains can be represented as a “DNA-type”, where two intertwined helices based on Ag–Ochelate and Ag–Cα bonds are connected through Ag–Obridge ones. Two structural types of chain coordination polymers, [Ag(tfac)(CH3CN)] and [Ag2(L)2(solvent)], have been revealed for the adducts. The latter structural type differs significantly from the previously studied toluene and acetonitrile adducts of fluorinated Ag(I) β-diketonates of the same stoichiometry. Thermal analysis in helium showed that both 1 and 2 decompose to metallic silver with the compound of pfpac-ligand being slightly more stable.  相似文献   

19.
A series of six seven-coordinate pentagonal-bipyramidal (PBP) erbium complexes, with acyclic pentadentate [N3O2] Schiff-base ligands, 2,6-diacetylpyridine bis-(4-methoxybenzoylhydrazone) [H2DAPMBH], or 2,6-diacethylpyridine bis(salicylhydrazone) [H4DAPS], and various apical ligands in different charge states were synthesized: [Er(DAPMBH)(C2H5OH)Cl] (1); [Er(DAPMBH)(H2O)Cl]·2C2H5OH (2); [Er(DAPMBH)(CH3OH)Cl] (3); [Er(DAPMBH)(CH3OH)(N3)] (4); [(Et3H)N]+[Er(H2DAPS)Cl2] (5); and [(Et3H)N]+[Y0.95Er0.05(H2DAPS)Cl2] (6). The physicochemical properties, crystal structures, and the DC and AC magnetic properties of 1–6 were studied. The AC magnetic measurements revealed that most of Compounds 1–6 are field-induced single-molecule magnets, with estimated magnetization energy barriers, Ueff ≈ 16–28 K. The experimental study of the magnetic properties was complemented by theoretical analysis based on ab initio and crystal field calculations. An experimental and theoretical study of the magnetism of 1–6 shows the subtle impact of the type and charge state of the axial ligands on the SMM properties of these complexes.  相似文献   

20.
Calculations of the C3H6 · LiH, C4H8 · M+, and C4H8 · MH systems and of C2H2 · MH complexes (M = Li or Na) were carried out by the unrestricted Hartree-Fock-Roothaan (UHF) method with partial optimization of the geometry using fixed geometric parameters of the C3H6 and C4H8 molecules. The standard 3-21G and 6-31G* basis sets were used. Unlike the C3H6 · LiH structure, the C4H8 · M+ and C4H8 · MH systems are typical complexes. It was found that the C4H8 · M+, C4H8 · MH, and C2H2 · MH complexes are similar in coordination of M+ ions and MH molecules by carbon atoms in spite of considerable differences in the interatomic distances (–1 A) between these atoms in the C4H8 and C2H2 molecules. The heats of formation (Q), which were calculated in the UHF/6-31G* approximation and using second- and fourth-order Möller-Plesset perturbation theory taking into account the electron correlation energy in the MP2/6-31G*. MP4(SDQ)/6-31G*, and MP4(SDTQ)/6-31G* approximations, satisfy the following relationships: Q(C2H3 · MH) < Q(C4H8 · MH) < Q(C4H8 · M+). It was observed that in going from Li to Na the corresponding values of Q tend to decrease.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 7, pp. 1636–1640, July, 1996.  相似文献   

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