Multiscale Computer Simulations for Prediction of Thermophysical Properties and Phase Equilibrium
Date Issued
2005
Date
2005
Author(s)
DOI
932218E002136
Abstract
In this project, we propose to utilize the novel concept of computational hierarchy for the prediction of the thermophysical properties of chemicals and complicated materials and their phase equilibria. The method employed is based on the computation of solvation free energy for a chemical species in solution. It is shown that both the vapor pressure and activity coefficient, two important properties for making phase equilibrium predictions, can be determined from the knowledge of solvation free energy. The focus in this project is the development of a new approach that significantly enhances the efficiency and accuracy in calculation of the long-range electrostatic interaction in implicit solvation calculations using the Polarizable Continuum Model (PCM) and its variants, C-PCM/COSMO and IEF-PCM, where the solvent electrostatics effects are represented by discrete apparent charges distributed on tesserae of the molecular cavity surface embedding the solute. In principle, the accuracy of these methods is improved if the cavity surface is tessellated to finer tesserae; however, the computational time is increased rapidly. We show that such undesired dependency between accuracy and efficiency is a result of inaccurate treatment the apparent charge self-contribution to the potential and/or electric field. By taking into account of the full effects due to the size and curvature of the segment occupied by each apparent charge, the error in calculated electrostatic solvation free energy is essentially zero for ions (point charge at the center of a sphere) regardless of the degree of tessellation for the solute. For amphiphilic molecules (approximated by a point charge located at a position away from the center of a sphere) the effects from the gradient of apparent charges become important. For such cases, we propose a multiple-sampling technique which lowers the calculated error by at least one order of magnitude compared to the original PCM methods.
Publisher
臺北市：國立臺灣大學化學工程學系暨研究所
Type
report
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