Molecular models for simulation of hydrogen fluoride

Molecular models of hydrogen fluoride (HF) are studied via molecular simulation. The importance of such a study extends from application in industries such as refrigerant production and semi-conductor processing to scientific understanding of phenomena related to hydrogen bonding. HF fluid properties are known to exhibit anomalous behavior including very large peaks in the vapor-phase heat capacity, an anomalous peak in the heat of vaporization, and low surface tension. All these anomalies originate in the significant hydrogen bonding occurring in the liquid and vapor. Application of molecular interaction models in simulation lends well to the advancing understanding of the HF system due to the wide range of available potential models, ab initio calculations, and essential experimental data for comparison.; The present study considers various molecular models, with particular interest in ab initio based models and polarizable models. A novel association-bias Monte Carlo method is developed to aid in the molecular simulation calculation of such intermolecular interaction models. The available molecular models (through literature and other sources) are investigated for their ability to capture structural and thermodynamic properties (in comparison to experiment). Weaknesses and strengths are surmised with intensions on producing better molecular model, not only for HF but other related molecules. A trimer-based polarization model is presented and analyzed with this in mind. An investigation is performed by comparing several interaction models (including ab initio energies) to the developed model. The insight is transferred to molecular simulation to examine fluid phase properties ranging from coexistence behavior to structural details.; In a study of non-ideal vapor-phase behavior, HF, water and their mixtures, are simulated at experimental temperature and saturation pressure to measure fugacity coefficients using several molecular models. Two similar methodologies are employed to calculate the fugacity coefficient. Compressibility factors and fugacity coefficients are compared to experiment for the pure HF and water systems. The extension of the methodology to the saturated mixture at experimental T and P is accomplished. The calculated fugacity coefficients are combined with experimental data to improve the thermodynamic consistency of derived activity coefficients.