SCI-PCM

The original PCM method uses a cavity made of spherical regions around each atom. The isodensity PCM model (IPCM) uses a cavity that is defined by an isosurface of the electron density. This is defined iteratively by running SCF calculations with the cavity until a convergence is reached. The self-consistent isodensity PCM model (SCI-PCM) is similar to IPCM in theory, but different in implementation. SCI-PCM calculations embed the cavity calculation in the SCF procedure to account for coupling between the two parts of the calculation. 

SCF (self-consistent field) procedure for solving the Hartree-Fock equations SCI-PCM (self-consistent isosurface-polarized continuum method) an ah initio solvation method... 

Compute the energies of the three structures using the SCI-PCM SCRF model and the B3LYP/6-31+G(d) model chemistry. ... 

Both the MP2 Onsager calculation and the IPCM calculaton are in good agreement with experiment. The SCI-PCM and Hartree-Fock Onsager SCRF calculations perform significantly less well for this problem. ... 

Over the years, many workers have addressed the problem of choice of cavity and the reaction field. Tomasi s polarized continuum model (PCM) defines the cavity as a series of interlocking spheres. The isodensity PCM (IPCM) defines the cavity as an isodensity surface of the molecule. This isodensity surface is determined iteratively. The self-consistent isodensity polarized continuum model (SCI-PCM) gives a further refinement in that it allows for a full coupling between the cavity shape and the electron density. 

Computational approach. Lee and Houk conducted calculations using a methyl-ammonium ion to mimic the key lysine of the enzyme active site.16 They chose this model because, even though no crystal structures had been solved at the time, a lysine was known to be essential for catalysis.60 The reaction of orotate + CH3NH3 to form a carbene-methylamine complex was thus examined in various dielectrics using the SCI-PCM SCRF method in Gaussian 94.30 31 48 Solvation energies computed at the RHF/6-31 + G level were used to correct gas phase MP2/ 6-31 + G energies and obtain AH values for reaction in solution. 

Molecular geometries were optimized using Gaussian03 at a DPT B3LYP/6-31G (2d,2p) level of theory using SCI-PCM solvation model (water). Effective core... 

In order to improve the relative energies we have also calculated single point energies of the stmctures of (i) reactants, (ii) intermediate and (iii) products of the reaction at B3LYP/6-31 -I- G level as well as at B3LYP/3-21G( ) employing SCI-PCM model... 

Figure 7. ZPE coirected SCI-PCM leactian surfaces for OH radical addition to the three ring carbons in imidazxjle (A) PMP2/6-3110(2df.p)//MP2/6-3 lG(d,p), (B) B3LYP/6-3110(2df.p)//B3LYP/6-3 lG(d,p)...

Solvent effects are taken into account using the super-molecule cluster model, by which the interaction between solute and a few solvent molecules is explicitly included, and bulk solvent effect is added through the polarized continuum models, such as PCM, conductor-like PCM (CPCM), iso-density PCM (IPCM), and self-consistent isodensity PCM (SCI-PCM), which were developed on the basis of the Onsager reaction field theory and are recognized... 

A full quantum-mechanical description of the Menshutkin reaction has been obtained for gas phase and solution by using density functional theory (DFT) and the self-consistent isodensity polarizable continuum model (SCI-PCM). Ammonia and pyridine were the nucleophiles and methyl chloride and methyl bromide, the electrophiles. In the gas phase an initial dipole complex intermediate is followed by a transition state leading to an ion pair. In the solvent-effect calculations, the dipole complex disappears with both cyclohexane and DMSO. The transition state is stabilized compared with the gas phase. The ion-pair product is strongly stabilized and in DMSO it is dissociated into free ions. 

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