Polarizable continuum model
The polarizable continuum model (PCM) is a commonly used method in computational chemistry to model solvent molecules. If it were necessary to consider each solvent molecule as a separate molecule, the computational cost of modeling a solvent-mediated chemical reaction would grow prohibitively high. Modeling the solvent as a polarizable continuum, and not as individual molecules, makes ab initio computation feasible.
The molecular free energy of solvent is computed as the sum of three terms:
- Gsol = Ges + Gdr + Gcav
- Ges = elecrostatic
- Gdr = dispersion-repulsion
- Gcav = cavitation[1]
The PCM solvation model is available for calculating energies and gradients at the Hartree-Fock and density functional theory (DFT) levels.[1]
The authors of a 2002 paper observe that PCM has limitations where non-electrostatic effects dominate the solute-solvent interactions. They write in the abstract: "Since only electrostatic solute-solvent interactions are included in the PCM, our results lead to the conclusion that, for the seven molecules studied, in cyclohexane, acetone, methanol, and acetonitrile electrostatic effects are dominant while in carbon tetrachloride, benzene, and chloroform other nonelectrostatic effects are more important."[2]
There is an integral equation formalism (IEF) version of the PCM (ref. 4 in the 2002 paper).
References
- ^ a b Hendrik Zipse (09.02.2004). http://www.cup.uni-muenchen.de/oc/zipse/lv18099/solv/pcm.html. Retrieved January 25, 2009.
{{cite web}}: Check date values in:|date=(help); Missing or empty|title=(help); Unknown parameter|Title=ignored (|title=suggested) (help) - ^ B. Mennucci et. al. "Polarizable Continuum Model (PCM) Calculations of Solvent Effects on Optical Rotations of Chiral Molecules." J. Phys. Chem. A 2002, 106, 6102-6113. Link to full text
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