VT Sigma Profile Databases
VT Sigma Profile Databases
Thermodynamic methods based on conductor-like screening models (COSMO) originated from the use of solvation thermodynamics and computational quantum mechanics. These methods rely on sigma profiles specific to each molecule. A sigma profile is a molecular-specific distribution of the surface-charge density, which enables the application of solvation-thermodynamic models to predict vapor-liquid and solid-liquid equilibria, and other properties. Two COSMO-based thermodynamic models are COSMO-RS (realistic solvation) developed by Klamt and his colleagues, and COSMO-SAC (segment activity coefficient) published by Lin and Sandler. Quantum mechanical calculations for generating the sigma profiles represent the most time-consuming and computationally expensive aspect of using COSMO-based methods. A growing number of scientists and engineers are interested in the COSMO-based thermodynamic models but are intimidated by the complexity of performing quantum mechanical calculations. We present two open literature databases, the VT-2005 Sigma Profile Database and the VT-2006 Solute Sigma Profile Database, that contain sigma profiles for 1,645 unique compounds. We design both of these databases for use with the conductor-like screening model ? segment activity coefficient (COSMO-SAC), a liquid-phase activity-coefficient model. The databases contain the necessary information to perform binary and multicomponent VLE and SLE predictions.
VT-2005 Sigma Profile Database
VT-2006 Solute Sigma Profile Database
*Direct correspondence to Dr. Y. A. Liu: (email@example.com)
Sigma Profile Summary
COSMO models require sigma profiles in a manner similar to the way UNIFAC requires parameter databases, with one exception: sigma profiles are molecule-specific whereas UNIFAC parameters are functional group-specific. Furthermore, UNIFAC requires binary interaction parameters for the functional group pairs (binary interactions between groups). As a result, a sigma-profile database is much smaller and easier to use than the UNIFAC parameter database. Sigma profiles require only the molecular structure and a density-functional theory calculation to incorporate new compounds into the database.
The COSMO model creates a cavity around a solute molecule and then ideally dissolves it into an infinite conducting medium. We summarize this process with this figure:
We calculate the surface charge distribution or the SIGMA PROFILE. The sigma profile shows the probability of a surface segment having a specific charge density that determines the interaction energy with other surface segments in the liquid phase.
This work also provides a FORTRAN program to generate additional sigma profiles, as well as a FORTRAN program to generate binary and multicomponent phase-equilibrium (VLE and SLE) predictions using the COSMO-SAC model. Our sigma profile database will facilitate predictions of thermodynamic properties and phase behaviors from COSMO-based thermodynamic models. We offer detailed tutorials and procedures for use with our programs so the reader may also use their own research as well.
Open Literature Resources
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FORTRAN Programs with Source code
VT-2005 Sigma Profile Database Files
VT-2006 Solute Sigma Profile Database Files