Polarizable continuum model iterative polarization

It is relatively straightforward to implement the polarizable continuum model (PCM) via Eq. (39).11 12,105,117 The potential of the reaction field, VCT(r), is due to the ostensible (virtual) charge distribution o(r) on the cavity surface, which in turn is related to the potential Vsoiutc(r) that arises from the nuclei and electrons of the solute molecule, Eq. (2). Since the latter is likely to be further polarized by VCT(r), thus affecting Vs0,utc(r), iteration to self-consistency is needed,105,106 as already has been pointed out. (However Montagnani and Tomasi suggest that this often has little practical consequence.)118... 

Note that using the polarizable continuum model (PCM) the dipole moment of acetone is calculated as 3.98 D with the sameMP2/aug-cc-pVDZ level. This is equivalent to the first average dipole moment, obtained in the first step (see Figure 7-12), and represents a polarization of 34%, about half of that obtained with the iterative process. This case indicates that the PCM calculation could be used as a good estimate of the polarization or for starting the iterative procedure. 

Alternatively, reaction field calculations with the IPCM (isodensity surface polarized continuum model) [73,74] can be performed to model solvent effects. In this approach, an isodensity surface defined by a value of 0.0004 a.u. of the total electron density distribution is calculated at the level of theory employed. Such an isodensity surface has been found to define rather accurately the volume of a molecule [75] and, therefore, it should also define a reasonable cavity for the soluted molecule within the polarizable continuum where the cavity can iteratively be adjusted when improving wavefunction and electron density distribution during a self consistent field (SCF) calculation at the HF or DFT level. The IPCM method has also the advantage that geometry optimization of the solute molecule is easier than for the PISA model and, apart from this, electron correlation effects can be included into the IPCM calculation. For the investigation of Si compounds (either neutral or ionic) in solution both the PISA and IPCM methods have been used. [41-47]... 

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