Transferable Intermolecular Potential Models for a Broad Range of Organic Compounds

Abstract

Vapor pressure and liquid density are used to characterize step potentials for fluorinated, chlorinated, brominated, and iodinated hydrocarbons, along with a variety other compounds, bringing the transferable database to 339 training compounds, 112 of which are added in this manuscript, and 25 “validation” compounds. The potentials were characterized by four-step potentials consistent with those of previous studies for the SPEADMD model. Vapor pressure deviations average near 10 % for most compounds in the training set and near 40 % for the validation set. Higher deviations appear in the validation set for compounds in which multiple functionalities are located in close proximity, indicating sensitivity to the transferability assumption in these cases. Deviations in liquid density approach 4 %, despite the large shifts in density caused by the relatively heavy halogenated atoms. The availability of transferable potentials for so many compounds sets the stage for systematic studies of phase behavior over a broad range of molecular types. In the context of this study, several key elements were identified for organizing the physical property database, simulation results, and analytical tools to infer optimal characterizations of the molecular interactions. The physical property database must be critically evaluated to eliminate extrapolations and ambiguous data. The directory structure must be flexible and extensible to accommodate continuous improvement as more data and more compounds are incorporated into the analysis. Finally, an efficient methodology must be implemented to permit optimal characterization of the molecular interactions in a reasonable time on a continuing basis. The methodology presented in this paper permits a fresh optimization of the entire database in roughly 12 h.