CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

1.2. Motivation
1.2.1. Macrosolvation versus Microsolvation
Though solvation process at the macroscopic level is well studied, only a little
effort has been given to understand the solvation process at the molecular level. Average
information about various interactions is obtained from macroscopic solvation study.
Information about coordination number, thermodynamic parameters (e.g. free energy,
enthalpy of solvation, etc), bulk detachment energy of excess electron from a solute, UV-
Vis spectra, etc, is obtained based on experiments carried out in the bulk solution. 1-3
Many theoretical models are available to study macroscopic solvation of chemical
species. Self consistent reaction field (SCRF) model due to Onsager –Kirkwood is one of
the simple and popular models to study the macroscopic solvation. 4-5 In this model a
spherical solute cavity is considered. Molecular shape cavity models like polarizable
continuum model (PCM), conductor like screening model (CPCM) are also available to
study the solvent effect at the macroscopic level. 6 There are two major advantages of
continuum models (implicit solvation models). The first one is the reduction in the
system’s number of degrees of freedom. The second advantage is that the continuum
models provide a very accurate way to treat the strong, long-range electrostatic forces
that dominate many solvation phenomena. The major drawback of these implicit
solvation models is that the explicit solvent effect is not taken into account. As a result,
molecular level information cannot be extracted based on studies carried out in the bulk
solution (macroscopic solvation) during the process of solvation. To understand different
molecular level interactions responsible for solvation, one has to study the microsolvation
by adding solvent molecules one by one following the bottom up approach. Studies on
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