Solvation Models
There are some methods which are established in order to observe the effect of solvation in a system. These models are distinguised as Polarizable Continuum Model or Implicit model, Explicit model and Hybrid Explicit Model. These three models subdivide and they will be discussed further. While using these models, the one which fits to the system should be chosen carefully since reducing the cost and time is very significant. When the time gets longer, more payment is done and also in a limited time performing a couple of models is much more better than performing just one system. Indeed, the efficiency and accuracy of the system is another aspect which shouldn’t be neglected too. Thus, while choosing the best model for the specified system the parameters which are refferd above should be evaluated in detailed and carefully. Before explaining the models in detail, some of the terms should be known by heart.
What is Solvation?

To understand the process of solvation, the terms solute and solvent should be known. Solute can be described as a substance which dissolves in a solvent and solvent is the substance which dissolves a solute. When a solute starts to dissolves in a solvent a polarization is observed in the solute in response to the solvent polarization as mentioned in the figure. In addition, a reorientation is observed in the solvent molecule due to the charges in the solute as indicated in the figure. Hence, an interaction happens between the solute and solvent molecules and the solute molecules or ions are surrounded by the solvent molecules . This interaction and association can be referred as solvation.( http://www.chemistrydaily.com/chemistry/Solvation)
Free Energy of Solvation
The meaning of free energy solvation is, the change in free energy of a molecule leaving the gas phase and entering a condensed phase, and is denoted as ΔGS0 [1]
The values of the free energy of solvation has a extensive range , hence it depends on the system which is constructed. There are some parameters which affect the solvation process and these are electrostatic interactions, cavitation, changes in dispersion, and changes in bulk solvent structure.[1]
To calculate the free energy of solvation there are some methods such as Potential Energy Surface, thermodynamic cycle and one dimensional slice.

Implicit Model
In Implict Model or the Polarizable Continuum model (PCM), the solvent which surrounds the solute, is represented with a continuus electric field that has all the thermodynamic properties of the solute. The electric field is reffered as the reaction field and in order to find the polarization energy in this field equation(?) is used. The polarization energy can be defined as the difference between the work of charging the system in the gas and solution phase and to obtain the polarization energy the electrostatic potential in the solution phase is required[1].
G=-12ρr∅rdr
In equation(?) G denotes polarizable energy, solute charge density and r is the discrete point charge [1].
Hence, to find the electrostatic potential some equations has developed.
Poisson Equation

Predicting Small-Molecule Solvation Free Energies: An Informal Blind Test for Computational Chemistry