J. C. Dobrowolsk et al.
102
If a solute does not form hydrogen bonds with a solvent, the calculations for solution
can be performed using a one of reliable PCm approaches. on the other hand, if a solvent molecule forms hydrogen bonds with a solute molecule, the use of PCm solvation
models is rather inappropriate. We have restricted our review mainly to the methods of
groups (II) and (III), i.e. continuum models and hybrid methods, treating the explicit
method only as a reference frame for them. For a detailed description of modelling
the solvent effect, we refer the Reader to the other reviews and books [54, 115–120].
5.4.3.1 Supermolecular Approach
to model the solvent effect, one explicitly treats the solute and solvent molecules
by quantum chemical methods. usually only the first solvation shell is considered;
therefore, this approach describes only short-range solvent effects. the geometries
of the solute–solvent cluster are usually found by means of a geometry optimisation
procedure. optimisation of the global and local minima is confirmed by ascertaining
that the harmonic frequencies are real. the conformer population of all minima found
is calculated by the use of the Boltzmann distribution under normal conditions and
Gibbs free energy differences (ΔG). The interaction energy is corrected for the Basis Set Superposition Error (BSSE) by the counterpoise method [121]. the energies
needed to deform the monomer from the optimised monomer geometries to those in
the cluster geometry can be estimated by a seven-point correction method [122, 123].
Long-range solvent effects can be accounted for by merging the supermolecular approach and one of the PCm models by placing the solute-solvent cluster in the cavity
of a dielectric medium. With an increasing number of solvent molecules, the level
of theory is necessarily reduced and nowadays the dFt method is the only choice.
5.4.3.2 Polarised Continuum Models
In this approach, the solvent S is mimicked by a continuous dielectric medium. the
solute molecule m (or a group of molecules) is represented by a charge distribution,
which occupies a given volume, called the molecular cavity. the solute molecule
polarises the solvent, which, as a response, induces an electric field called the “reaction field” (RF), interacting with the solute. the combination of the solute charge,
or the field it produces, and the solvent reaction field can be analytically treated to
give the interaction potential. only the effect of the long-range electrostatic interaction of the solute with the solvent reaction field is included in this model.
this general picture can be translated into a quantum mechanical language. the
solute is represented by its wavefunction. the interaction with the solvent is introduced in the hamiltonian through a perturbation, the reaction potential v R . Including this in the solute hamiltonian leads to a new, changed solute electronic structure
charge distribution. the Self-Consistent Reaction Field method (SCRF) is obtained
through an iterative procedure to self-consistency.
Implicit Polarised Continuum model (PCm) methods based on solvent reaction
field philosophy differ mainly in: (1) the cavity shape and (2) the way in which the
102
If a solute does not form hydrogen bonds with a solvent, the calculations for solution
can be performed using a one of reliable PCm approaches. on the other hand, if a solvent molecule forms hydrogen bonds with a solute molecule, the use of PCm solvation
models is rather inappropriate. We have restricted our review mainly to the methods of
groups (II) and (III), i.e. continuum models and hybrid methods, treating the explicit
method only as a reference frame for them. For a detailed description of modelling
the solvent effect, we refer the Reader to the other reviews and books [54, 115–120].
5.4.3.1 Supermolecular Approach
to model the solvent effect, one explicitly treats the solute and solvent molecules
by quantum chemical methods. usually only the first solvation shell is considered;
therefore, this approach describes only short-range solvent effects. the geometries
of the solute–solvent cluster are usually found by means of a geometry optimisation
procedure. optimisation of the global and local minima is confirmed by ascertaining
that the harmonic frequencies are real. the conformer population of all minima found
is calculated by the use of the Boltzmann distribution under normal conditions and
Gibbs free energy differences (ΔG). The interaction energy is corrected for the Basis Set Superposition Error (BSSE) by the counterpoise method [121]. the energies
needed to deform the monomer from the optimised monomer geometries to those in
the cluster geometry can be estimated by a seven-point correction method [122, 123].
Long-range solvent effects can be accounted for by merging the supermolecular approach and one of the PCm models by placing the solute-solvent cluster in the cavity
of a dielectric medium. With an increasing number of solvent molecules, the level
of theory is necessarily reduced and nowadays the dFt method is the only choice.
5.4.3.2 Polarised Continuum Models
In this approach, the solvent S is mimicked by a continuous dielectric medium. the
solute molecule m (or a group of molecules) is represented by a charge distribution,
which occupies a given volume, called the molecular cavity. the solute molecule
polarises the solvent, which, as a response, induces an electric field called the “reaction field” (RF), interacting with the solute. the combination of the solute charge,
or the field it produces, and the solvent reaction field can be analytically treated to
give the interaction potential. only the effect of the long-range electrostatic interaction of the solute with the solvent reaction field is included in this model.
this general picture can be translated into a quantum mechanical language. the
solute is represented by its wavefunction. the interaction with the solvent is introduced in the hamiltonian through a perturbation, the reaction potential v R . Including this in the solute hamiltonian leads to a new, changed solute electronic structure
charge distribution. the Self-Consistent Reaction Field method (SCRF) is obtained
through an iterative procedure to self-consistency.
Implicit Polarised Continuum model (PCm) methods based on solvent reaction
field philosophy differ mainly in: (1) the cavity shape and (2) the way in which the