Solvent Effects. 5. Influence of Cavity Shape, Truncation of Electrostatics, and Electron Correlation on ab Initio Reaction Field Calculations

Abstract

We describe several improvements to the reaction field model for the ab initio determination of solvation effects. First, the simple spherical cavity model is expanded to include higher-order electrostatic interactions. Second, two new and efficient implementations of the polarizable continuum model (PCM) are described, which allow a more realistic specification of the solute cavity as well as infinite-order electrostatics. Electron correlation effects are evaluated using the B3LYP density functional and Möller−Plesset perturbation theory to second order. An assessment of the importance of these various factors is made by comparing theoretical results to the experimentally known conformational equilibrium between syn and anti forms of furfuraldehyde and the C−C rotational barrier of (2-nitrovinyl)amine. Comparisons are also made with calculations that employ an ellipsoidal cavity with sixth-order electrostatics. Optimization using a simple Onsager model appears to be sufficient to evaluate the important geometry changes in solution. Energies obtained from the spherical and ellipsoidal cavity models often exhibit poor convergence in the truncated electrostatic series. Correlation to experiment is much improved when an infinite-order PCM method is used.

The Energetics for Hydrogen Addition to Naphthalene Cations

“…The geometry and zero-point energies for the reaction in ice are determined using the Onsager model (Onsager 1936;Wong et al 1992) using water as the solvent. The energetics are determined using the static isodensity surface polarized continuum model (Foresman et al 1996; IPCM). For the IPCM studies, we use two values for the static dielectric constant ( ) of water, namely 78.38 and 2.…”

On the cis -> trans isomerization of the square-planar [Pt(Cl)(SnCl3)(PH3)2] compound: ab initio gas phase reaction mechanism and solvent effects using continuum models

“…Using this approach, we obtained a cavity radius a 0 of 4.472 Å for the Cis isomer, 4.099 Å for the Trans isomer and 4.196 Å for TS. The other method used to study the solvent effects was the IPCM (Isodensity Polarizable Continuum Model) 20 , which uses a more realistic molecular-shape cavity, derived from the solute electron density. This method overcomes two main deficiencies of the SCRF approach: the assumption of a uniform charge distribution and the symmetric shape of the cavity.…”

“…These methods can be classified according to the form they treat explicitly the solutesolvent interactions, such as Molecular Mechanics force fields (MM) 15 , Empirical Valence Bond method (EVB) 16 and the whole variation of hybrid Quantum Mechanics/ Molecular Mechanics potentials (QM/MM) 17 . The other models are based on an implicit approach, which treats the solvent as a dielectric continuum medium in which the solute molecule is surrounded by a cavity, such as the Self Consistent Reaction Field method (SCRF) 18 , the Polarizable Continuum Model (PCM) 19 , the Isodensity Polarizable Continuum Model (IPCM) 20 and the Generalized Conductor-like Screening Model (GCOSMO) 21 . The implicit and explicit approaches to treat the solute-solvent interactions have been successfully applied to understand the role of the solvent in some relevant organic reactions 22 .…”

Solvent effects on 2-methoxyethanol conformers: an ab initio DFT study using the SCI-PCModel

“…For the identification of the atoms in structural parameters, a left-to-right order of the italicized atomic symbols in C(H 3 )OC(H 2 )C(H 2 )OH is adopted. Ab initio calculations were carried out at the B3LYP/6-311ϩG(3df,2df,2p)//B3LYP(6-31G(d) level, within the framework of SCRF (Self-Consistent Reaction Field) theory, using the SCI-PCModel (Self-Consistent Isodensity Polarized Continuum Model) [5,6]. The GAUSSIAN 94W program package [7] was used in the calculations.…”