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Overview
The COSMO-RS (COnductor like
Screening MOdel for Realistic Solvents) Module developed by Klamt 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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