Abinitio study on radical anions of nitro compounds

1992 ◽  
Vol 70 (2) ◽  
pp. 314-326 ◽  
Author(s):  
Fabio Ramondo
Keyword(s):  
Correlation Energy ◽  
Nitro Compounds ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Radical Anions ◽  
Electron Correlation Energy ◽  
Structural Differences ◽  
Moller Plesset ◽  
Planar Electron ◽  
Abinitio Calculations

The results of abinitio molecular orbital calculations on some nitro compounds, RNO2 (R = CH3, CF3, CH2F, BH2, BF2, BHF, C6H5) and on the corresponding radical anions are reported. The geometries of the neutral and charged species were optimized at the SCF and MP2 levels of theory employing the 6-31G* and the 6-31 + G* basis sets. The rotation about the CN and BN bonds reveals distinct conformations for each molecule and vibrational frequencies were determined for such structures. All the employed levels of theory predict structural differences between neutral and charged molecules. The major geometrical changes occurring by electron adding to RNO2 consist in the lengthening of the NO bonds and in the shortening of the CN and BN bonds. The radical anions are calculated to be pyramidal at nitrogen in the stable conformers of CH3NO2−, CF3NO2−, CH2FNO2−, while, for the π-electron-accepting substituents (BH2, BHF, BF2, C6H5), the anion is planar. Electron correlation energy corrections in the framework of Møller–Plesset perturbation theory were included to determine relative stabilities between different conformations. At the MP4/6-31G*//MP2/6-31G* level, an easy rotation of the NO2 group is predicted for all the radical anions and neutral molecules with the exception of BH2NO2−, BF2NO2−, and BHFNO2−, which show high torsional barriers about the BN bond. Keywords: nitro compounds, radical anions, abinitio calculations, molecular structure.

Theoretical investigation of the oxidation pathways of HO•-initiated reactions of acrolein, methacrolein, and trans-crotonaldehyde

2009 ◽  
Vol 87 (12) ◽  
pp. 1716-1726 ◽  
Author(s):  
Sabry El-Taher
Keyword(s):  
Double Bond ◽  
Transition State ◽  
Correlation Energy ◽  
Single Point ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Methyl Substitution ◽  
Reactive Complex ◽  
Moller Plesset ◽  
Transition State Structures

Ab initio molecular-orbital calculations have been performed to investigate the reaction mechanisms of the HO•-initiated reactions of the α,β-unsaturated aldehydes: acrolein (ACR), methacrolein (MACR), and trans-crotonaldehyde (CROT). All geometries were fully optimized at the MP2(Full)/6–31G(d,p) level. The correlation energy corrections were introduced by carrying out single-point calculations using both spin-projected second-order Møller–Plesset perturbation theory (PMP2) and coupled-cluster theory (CCSD(T)) using basis sets of different sizes. All reaction pathways studied proceed via a barrierless formation of a loosely bound pre-reactive complex in the entrance channel. The transition-state structures of the HO• additions to the terminal (β) and to the central (α) carbon atoms of the C=C double bond are found to be reactant-like structures. The lowest-energy barrier pathways are found to be the aldehydic H-atom abstraction. The β-addition pathways are found to be energetically more favored than the α-addition pathways. The HO• addition and aldehydic H-atom abstraction pathways are found to be highly exoergic, with the H-atom abstraction pathway being more exoergic than the addition pathways. Although the methyl substitution at the C=C double bond of methacrolein and crotonaldehyde lowers the energies of the transition-state structures of both α- and β-addition pathways, it destabilizes the energies of the transition-state structures of the corresponding aldehydic H-atom abstraction pathways, compared with that of acrolein.

Theoretical study on the insertion reaction of CH(X2Π) with CH4

1997 ◽  
Vol 75 (7) ◽  
pp. 996-1001 ◽  
Author(s):  
Zhi-Xiang Wang ◽  
Ming-Bao Huang. ◽  
Ruo-Zhuang Liu
Keyword(s):  
Electron Correlation ◽  
Energy Surface ◽  
Theoretical Study ◽  
Reaction Path ◽  
Basis Sets ◽  
Insertion Reaction ◽  
Molecular Orbital Calculations ◽  
Insertion Reactions ◽  
Moller Plesset ◽  
Ch Radical

The CH + CH4 reaction has been studied by means of ab initio molecular orbital calculations incorporating electron correlation with Møller–Plesset perturbation theory up to second and fourth orders with the 6-31G(d,p) and 6-311++G(2d,p) basis sets. An energetically feasible insertion reaction path has been found in the potential energy surface that confirms the experimental proposal for the mechanism of the CH + CH4 reaction. The feature of the mechanism for the CH + CH4 insertion reaction is found to be different from the feature of the mechanisms for the CH + NH3, CH + H2O, and CH + HF insertion reactions, but somewhat similar to that for the CH2 + CH4 insertion reaction. Energetic results for the CH + CH4 reactions are in agreement with experiment. Keywords: CH radical, methane, reaction mechanism.

AB INITIO CALCULATIONS OF INTERMOLECULAR INTERACTION POTENTIALS OF FULLERENE-FRAGMENTS SYSTEMS

2005 ◽  
Vol 04 (01) ◽  
pp. 49-58 ◽  
Author(s):  
YUKIUMI KITA ◽  
KEI WAKO ◽  
ISAMU OKADA ◽  
MASANORI TACHIKAWA
Keyword(s):  
Ab Initio ◽  
Intermolecular Interaction ◽  
Correlation Energy ◽  
Basis Set ◽  
Basis Sets ◽  
Cubic Phase ◽  
Molecular Orbital Calculations ◽  
Interaction Potentials ◽  
Basis Set Superposition Error ◽  
Intermolecular Distances

We have performed the ab initio molecular orbital calculations for combinations of the fullerene-fragments as the models of the nonbonding interaction of C 60 dimer at the preferred configurations in the simple cubic phase. The intermolecular interaction potentials have been calculated using several basis sets with MP2 level of the electron correlation energy and the basis set superposition error correction. The strong dispersion attractions that is dominant in the van der Waals interaction has been found for the combinations of the fullerene-fragments. The equilibrium intermolecular distances obtained are in good agreement with the corresponding experimental value. The repulsive region of the intermolecular interaction calculated by ab initio method is found to be express by an atom–atom interaction potential with an anisotropic exponential type repulsive term, which is less steep than the conventional Lennard–Jones type potential.

An approximate ab initio method based on the DIM model

2000 ◽  
Vol 78 (12) ◽  
pp. 1575-1586 ◽  
Author(s):  
John M Cullen
Keyword(s):  
Ab Initio ◽  
Excited States ◽  
Electron Correlation ◽  
Correlation Energy ◽  
Basis Sets ◽  
Ab Initio Method ◽  
First Order ◽  
Hartree Fock ◽  
Modified Method ◽  
Electron Correlation Energy

Using a second quantized formulation, an approximate diatomics in molecules (DIM) theory is presented in which all three- and four-centered electronic integrals are neglected. To ameliorate the effects of this approximation, the DIM one electron operator is constructed so that the true ab initio first-order density matrix and total energy are reproduced at the Hartree–Fock level. The resulting model was extensively tested for a variety of basis sets for its capability of capturing both the dynamic and nondynamic components of the electron correlation energy as well as the energies of excited electronic states. A modified method in which the DIM one-electron operator is formed from the initial extended Hückel guess of the Hartree–Fock orbitals was also found to produce excellent results.Key words: DIM, electron correlation energy, excited states, semiempirical.

An ab initio study on the reaction of CH(X2π) with CH4

1993 ◽  
Vol 71 (4) ◽  
pp. 512-519 ◽  
Author(s):  
Zhonghua Yu ◽  
Congxiang Chen ◽  
Mingbao Huang
Keyword(s):  
Ab Initio ◽  
Correlation Energy ◽  
Reaction Path ◽  
Addition Reaction ◽  
High Energy ◽  
Insertion Reaction ◽  
Molecular Orbital Calculations ◽  
Configuration Interaction Method ◽  
State Abstraction ◽  
Moller Plesset

The mechanism of the reaction CH(X2π) + CH4 has been investigated by ab initio molecular orbital calculations. Addition, insertion, and abstraction–addition reaction paths have been examined by, in total, five methods of approach. The addition reaction path has a rather high energy barrier. Our calculations have implied that the assumed insertion reaction path does not seem to exist for the reaction CH + CH4, and a two-step mechanism (abstraction–addition reaction path) was then proposed. For the abstraction–addition reaction, the reactants, transition state, intermediates, and products were optimized at the HF/3-21G and HF/6-31G* levels, and vibrational frequencies were calculated at the HF/3-21G level. Electronic correlation energy was estimated by means of the Møller–Plesset perturbation theory and configuration interaction method. The excited-state abstraction reaction was also studied in some detail.

Atomic Partitioning of the MPn (N=2,3,4) Dynamic Electron Correlation Energy by the Interacting Quantum Atoms (IQA) Method: A Fast and Accurate Electrostatic Potential Integral Approach

2019 ◽  
Author(s):  
Mark A. Vincent ◽  
arnaldo silva ◽  
Paul Popelier
Keyword(s):  
Force Field ◽  
Electrostatic Potential ◽  
Electron Correlation ◽  
Correlation Energy ◽  
Integral Approach ◽  
Electron Correlation Energy ◽  
Order Of Magnitude ◽  
Interacting Quantum Atoms ◽  
Moller Plesset

The calculation of Moller-Plesset electron correlation energy of a topological atom interacting with its environment is now sped up by about an order of magnitude. Secondly, the proposed algorithm generates much more accurate energies for modest quadrature grids. Thus it becomes now possible to provide the training of the force field FFLUX with electron correlation energies.

Ab initio Computational Insight into the Interaction of Alkyl-substituted Ethene and Sulfenyl Halide

2011 ◽  
Vol 66 (8) ◽  
pp. 850-856 ◽  
Author(s):  
Ausra Vektariene ◽  
Gytis Vektaris
Keyword(s):  
Ab Initio ◽  
Ring Opening ◽  
Correlation Energy ◽  
Intrinsic Reaction Coordinate ◽  
Energy Profiles ◽  
Electron Correlation Energy ◽  
Reaction Proceeds ◽  
Mechanism Of Interaction ◽  
Moller Plesset ◽  
Insight Into

The ab initio calculations approach was used to determine the mechanism of interaction between propene and a sulfenyl halide. The second-order Møller-Plesset corrections for the electron correlation energy were applied to calculate the most probable Gibbs Free Energy profiles for the selected reaction. All optimized structures were confirmed by vibrational frequency analysis and intrinsic reaction coordinate calculations. Two possible reaction pathways were proposed and evaluated to conclusively characterize the reaction. The reaction proceeds via formation of a cyclic episulfonium intermediate, stereoselective ring opening of the episulfonium intermediate by the chloride anion, and isomerization of the adduct of the kinetically controlled reaction into the thermodynamically favorable product.

Atomic Partitioning of the MPn (N=2,3,4) Dynamic Electron Correlation Energy by the Interacting Quantum Atoms (IQA) Method: A Fast and Accurate Electrostatic Potential Integral Approach

2019 ◽  
Author(s):  
Mark A. Vincent ◽  
arnaldo silva ◽  
Paul Popelier
Keyword(s):  
Force Field ◽  
Electrostatic Potential ◽  
Electron Correlation ◽  
Correlation Energy ◽  
Integral Approach ◽  
Electron Correlation Energy ◽  
Order Of Magnitude ◽  
Interacting Quantum Atoms ◽  
Moller Plesset

The calculation of Moller-Plesset electron correlation energy of a topological atom interacting with its environment is now sped up by about an order of magnitude. Secondly, the proposed algorithm generates much more accurate energies for modest quadrature grids. Thus it becomes now possible to provide the training of the force field FFLUX with electron correlation energies.

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