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Overview
The COSMO-RS (COnductor
like Screening MOdel for Realistic Solvents) Module
developed by Klamat et al [1-3] allows the
prediction of properties of pure liquids and liquid
mixtures, such as:
- activity coefficients
- solubilities
- partition
coefficients
- excess energies
- boiling points
- vapor-liquid diagrams
The COSMO-RS module is available
in the current commercial ADF2007.01d release of
ADF. The ADF2007.01d release is available for
a limited number of platforms only including
Windows, Linux, Mac OS X.
Introduction:
The COSMO-RS (COnductor like
Screening MOdel for Realistic Solvents) was
developed by Klamt and coworkers [1-3]. There are
different implementations of COSMO-RS or
derivatives, and different parametrizations. The
method used in ADF is the one developed by Klamt et
al., and is described in detail in Ref. [2], and is
called here COSMO-RS. It is possible to use a
thermodynamically consistent combinatorial
contribution to the chemical potential as is used
in Ref. [3], and a temperature dependent hydrogen
bond interaction, also described in Ref. [3]. The
parameters in the paper [2] were reparametrized for
ADF. The ADF COSMO-RS command line program is
called crs. The main
authors of this program are Cory Pye (Saint Mary's
University, Halifax NS Canada) and Jaap Louwen
(Albemarle Corporation).
COSMO-RS uses the intermediate
results from quantum mechanical (QM) calculations
on individual molecules to predict thermodynamic
properties of mixtures of these molecules, for
example, solubility. There are a fair number of
reports of accurate prediction by COSMO-RS of
thermodynamic properties in general in the
literature. Many of these have been written by
Klamt and co-workers, see Ref. [3] and references
therein.
There are also empirical methods
like UNIFAC that can predict thermodynamic
properties (including the activity coefficients).
These methods contain group specific parameters and
are parametrized against a large data base. They
will often do better than COSMO-RS methods
(especially, of course, if the system of interest
was part of the data base used for parameter
estimation). However, these methods cannot handle
every type of molecule. In particular when unusual
combinations of functional groups occur (such as in
drug molecules), no parametrization is available.
COSMO-RS methods, on the other hand, only feature
general parameters not specific to chemical groups
or functionalities. All that is required is that a
quantum mechanical calculation can be done on the
molecule. Therefore, COSMO-RS can be a valuable
tool for the prediction of chemical engineering
thermodynamical properties, like, for example,
partial vapor pressures, solubilities, and
partition coefficients. An additional advantage of
COSMO-RS over empirical methods is that the
molecules dissolved may in fact be transition
states of a chemical reaction. This follows from
the fact that all that is required is that one can
do a QM calculation on the solute and QM on a
transition state has become standard in the last
two decades. This affords a unique opportunity to
predict the thermodynamics of a reaction including,
for instance, the balance between kinetically and
thermodynamically favored reaction pathways as a
function of the solvent used.
References
1. A. Klamt, Conductor-like
Screening Model for Real Solvents: A New Approach
to the Quantitative Calculation of Solvation
Phenomena, J. Phys. Chem. 99 (1995)
2224.
2. A. Klamt, V. Jonas, T.
Bürger and J.C. Lohrenz, Refinement and
Parametrization of COSMO-RS, J. Phys. Chem. A
102 (1998) 5074.
3. A. Klamt, COSMO-RS From
Quantum Chemistry to Fluid Phase Thermodynamics and
Drug Design, Elsevier, Amsterdam (2005), ISBN
0-444-51994-7.
4. B. Delley, The conductor-like
screening model for polymers and surfaces,
Molecular Simulation 32 (2006)
117.
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