Electron correlation intramolecular

Floating point, 276 Fluorine, ion, electronic correlation energy, 240 London energy, 78 molecules, intramolecular London energies, 78... 

These surfaces are all based on some combination of ab initio electronic structure calculations plus fitting. The AD and BM surfaces are based respectively in whole or in part on extended-basis-set single-configuration self-consistent-field calculations, whereas the RB and RBST calculations are based on calculations including electron correlation by Moller-Plesset fourth-order perturbation theory. For the rigid-rotator calculations R., the intramolecular internuclear distances R- and R ... 

Teppen, B. J., M. Cao, R. F. Frey, C. Van Alsenoy, D. M. Miller, and L. Schafer. 1994a. An Investigation into Intramolecular Hydrogen Bonding Impact of Basis Set and Electron Correlation on the Ab Initio Conformational Analysis of 1,2-Ethanediol and 1,2,3-Propanetriol. J. Mol. Struct. (Theochem) 314,169-190. 

The dispersive force arises due to the intermolecular electron correlation between the solute and the solvent. Further, it is also important to include the changes in intramolecular and intermolecular solvent electron correlation upon insertion of the solute in the solvent continuum. Further, electron correlation affects the structure of the solute and its charge distribution. Hence, the wave function obtained from the calculation with electron correlation provides a more accurate description of reaction field. 

Significant changes in optimized geometries due to electron correlation contributions are also of relevance for systems which present intramolecular hydrogen bonds. We shall present here, as a suitable example, the case of monothiomalonaldehyde (la) and its thienol tautomer (lb), since in this case the characteristics of the intramolecular hydrogen bonds depend strongly on the inclusion of electron correlation effects in the theoretical treatment. 

Chipot C, Rinaldi D, Rivail JL (1992) Intramolecular electron correlation in die self-consistent reaction field model of solvation. A MP2/6-31G ab initio study of the NH3—HC1 complex. Chem Phys Lett 191 287- 292... 

Intramolecular nucleophilic substitution to form thiiranes was studied by means of ab initio MO computations based on the 6-31G basis set <1997JCC1773>. Systems studied included the anions SCH2CH2F and CH2C(=S)CH2F which would afford thiirane and 2-methylenethiirane, respectively (Equations Z and 3). It was important to include electron correlation which was done with the frozen-core approximation at the second-order Moller-Plesset perturbation level. Optimized structures were confirmed by means of vibrational frequency calculations. The main conclusions were that electron correlation is important in lowering AG and AG°, that the displacements are enthalpy controlled, and that reaction energies are strongly dependent on reactant stabilities. 

The combination of H2CO with HCl was considered, along with two different approaches to electron correlation, by Rice et al.. The harmonic frequencies they predicted for the intramolecular modes at various levels are reported in Table 3.57, along with the changes induced by formation of the H-bonded complex. The numbering scheme was taken directly... 

C. Chipot, D. Rinaldi, and J.-L. Rivail, Chem. Phys. Lett., 191, 287 (1992). Intramolecular Electron Correlation m the Self-Consistent Reaction Field Model of Solvation. A MP2/6-31G Ab Initio Study of the NH,-HC1 Complex. 

Recently, a new theoretical method of calculating potential energy and dipole/polarizability surfaces for van der Waals molecules based on symmetry-adapted perturbation theory (sapt) of intermolecular forces (12)— (15) has been developed (16)-(24). In this method, referred to as many-body symmetry-adapted perturbation theory, all physically important contributions to the potential and the interaction-induced properties, such as electrostatics, exchange, induction, and dispersion are identified and computed separately. By making a perturbation expansion in the intermolecular interaction as well as in the intramolecular electronic correlation, it is possible to sum the correlation contributions to the different physical... 

In contrast, species with dithiadiazolylium rings in close proximity, e.g., [84][AsF6]2 and [85][AsF6]2, show strong intramolecular electron correlation and have two discrete, one-electron, reversible reductions to the radical cation and the diradical [92JCS(D)859]. 

A further difficulty arises because the exact waveflmctions of the isolated molecules are not known, except for one-electron systems. A common starting point is the Hartree-Fock wavefunctions of the individual molecules. It is then necessary to include the effects of intramolecular electron correlation by considering them as additional perturbations. Jeziorski and coworkers [66] have developed and computationally implemented a triple perturbation theory of the symmetry-adapted type. They have applied their method, dubbed SAPT, to many interactions with more success than might have been expected given the fundamental doubts [67] raised about the method. SAPT is currently both useful and practical. A recent application [68] to the CO2 dimer is illustrative of what can be achieved with SAPT, and a rich source of references to previous SAPT work. 

The purpose of the present study is to determine the conformational preference of 2-hydraxy-acetamide using ab initio quantum chemical methods. Intramoleculeur hydrogen-bonding is believed to have a strong influence on the relative stability of the conformers. The study of intramolecular hydrogenbonding by ab initio quantum chemical calculations is made difficult by the approximation techniques which are necessary for a theoretical description of a system such as this. The small energy differences calculated by ab initio quantum mechanical techniques are very sensitive to the choice of basis set used to parametrize the orbitals and to the calculation of electron correlation effects. 

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