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An investigation is carried out on the conformation of n-octadecane and its solvation shell in water, methanol and their mixtures using particle-based Monte Carlo simulations. A detailed analysis of hydrogen-bonding and enrichment of methanol around the solute provides further insight on the solvation process.

An extension of the transferable potentials for the phase equilibria united-atom (TraPPE-UA) force field to thiol, sulfide, and disulfide functionalities and thiophene is described. The binary vapor-liquid equilibrium data, as predicted by the TraPPE-UA force field, for the n-butane-(1)+ethanethiol(2) and 1-propanethiol(1)+n-hexane(2) systems show good experiment for the separation factors, however, the overprediction of the pure-component vapor pressure results in somewhat shifted coexistence curves.

The conformation effects on the sigma profiles, the vapor pressure predictions, and the vapor-liquid equilibrium (VLE) predictions were investigated for 1-hexanol, and 2-methoxy-ethanol. The results showed that the sigma profile for 1-hexanol varies only slightly using different conformations, while the sigma profile of 2-methoxy-ethanol shows a significant difference between the liquid and vapor phases.

The transferable potentials for phase equilibria force fields are extended to amine, nitro, nitrile, and amide functionalities and to pyridine and pyrimidine. Stimulations in the Gibbs ensemble were applied to neat amine, nitromethane, nitroethane, nitrobenzene, acetonitrile, propionitrile, acetamide, propanamide, butanamide, pyridine, and pyrimidine.

The extension of the transferable potentials for phase equilibria-united atom (TraPPE-UA) force field to the ether, glycol, ketone, and aldehyde functionalities is presented. Also, the structures of hydrogen-bonded aggregates were investigated for 1,2-ethanediol and 2-methoxyethan-1-ol, where the average hydrogen bond energies were found to be about -20 and -14 kJ mol(super -1) for inter- and intramolecular hydrogen bonds, respectively.

A novel Monte Carlo method, called the aggregation-volume-bias Monte Carlo algorithm (AVBMC), is presented, which greatly enhances the efficiency of sampling the phase space of fluid systems consisting of strongly associating molecules. The efficiency of AVBMC algorithm is demonstrated for a large variety of processes and systems, including the vaporization of a liquid methane droplet or a water cluster, an investigation of the temperature-and pressure-dependent properties of super heated hydrogen fluoride vapor, and the vapor-liquid coexistence curve of acetic acid.

Research is presented concerning the computation of temperature-composition and pressure-composition phase diagrams for four molecular models of a binary mixture of supercritical ethane and n-heptane. Comparison with a binary mixture of helium and n-heptane is made.

Simulation experiments demonstrate predicting the relative retention times of 10 alkane isomers based on their topology in a helium-squalane gas-liquid chromatographic system.

The solubilities of small solutes in normal alkanes depend on the solvent chain length. Gibbs-ensemble Monte Carlo simulations were conducted to investigate the vapor-liquid partitioning of methane in normal alkanes and related model solvents. The simulations revealed that the increase in solvent density with increasing solvent chain length is the main cause of the solvent chain length dependence for normal alkanes.

A study was conducted to analyze the performance of several all-atom force fields for alkanes. The vapor-liquid phase equilibria for methane, ethane, n-pentane, n-butane and n-octane was determined using configurational-bias Monte Carlo methods in the Gibbs ensemble. Experimental results indicated that the force fields exhibited larger deviations from experimental results for ethane. Findings also showed that the liquid structure was not very helpful in determining parameters between the alkane force fields.

A study was conducted to analyze a novel set of united-atom Lennard-Jones interaction parameters for n-alkanes from fitting to critical temperatures and saturated liquid densities. Simulations were performed for system sizes ranging from 400 molecules for methane to 200 molecules for n-dodecane. Experimental results indicated that for fields were unable to reproduce experimental second virial coefficients.

The time dependent changes in the intermolecular solvent response following resonant excitation of Coumarin 102 (C102) measured in acetonitrile-water binary mixtures is reported. The results show that the excitation of C102 simultaneously weakens and strengthens hydrogen bonding in complexes with two inequivalently bound waters.

The explicit hydrogen version of the transferable potentials for phase equilibria (TraPPE-EH) force field is extended to benzene, pyridine, diazenes and five-membered aromatic heterocycles with sulfur, oxygen and nitrogen heteroatoms. The extension of the TraPPE-SH force field with five new Lennard-Jones sites has described the vapor-liquid equilibrium properties of benzene and the aromatic heterocycles.

The thermodynamic properties of Al are calculated for two nonpairwise-additive potentials by using Monte Carlo simulations. The results have shown that the melting point for the embedded-atom model is higher than the experimental value and the embedded-atom (EAM) potential has yielded improved binding energies for smaller clusters, a small fraction of aggregates in the saturated vapor phase, and hence an accurate heat of vaporization and boiling point.

A research addressing a comprehensive particle-based simulation study of the structural, dynamic, and electronic properties of the liquid-vapor interface of water utilizing both ab initio and empirical models is illustrated. Numerous properties such as interfacial width, hydrogen bond populations, dipole moments, and correlation times will be characterized with identical schemes to draw useful conclusions on the strengths and weakness of the proposed models for interfacial water.

Configurational-bias Monte Carlo simulations in the Gibbs ensemble demonstrate that a diverse spectrum of hydrogen-bonded aggregates exists in dry and wet 1-octanol. Calculated partition constants quantify the influence of water saturation on the solubility characteristics of the dry and wet octanol phases.

Monte Carlo simulations are used to investigate the solvation of naphthalene in supercritical carbon dioxide at a temperature of 308.38 K at pressures 74.6, 79.7, 87.8 and 310.2 bar. Structural analysis through radial distribution functions and the corresponding number integrals yields good agreement with neuron diffraction data and shows evidence for a long-range density enhancement around solutes but lacking any specific solute-solvent clustering.

The retention mechanism of alcohols in a dioctyl ether retentive (stationery) phase from the molecular level is examined. The increase in temperature leads to a substantial decline in the separation factor between primary and secondary alcohols.

Vapor-liquid and vapor-solid coexistence curves were determined for benzene applying Gibbs ensemble Monte Carlo simulations to a 6-site united-atom and a 9-site model with explicit quadrupolar interactions. Although the 6-site model yields an adequate description of the vapor-liquid coexistence curve, it does not allow for a sufficient energetic gain for benzene I structure and the triple point temperature is underestimated by about 130 K.

Configurational-bias Monte Carlo simulations in the Gibbs ensemble are carried out to investigate the vapor-liquid-liquid equilibria and microscopic structures for two ternary systems. The simulations yield asymmetric compositions for the coexisting liquid phases and different degrees of microheterogeneity as measured by local mole fraction enhancements.

A series of first principles molecular dynamics and Monte Carlo simulations were carried out for liquid water to investigate the reproducibility of different sampling approaches. The computational benefits of CPMD sampling over Born-Oppenheimer sampling for structural and thermodynamic properties are appreciable for liquid water and arise from the substantial reduction time per step.

Gibbs free energies, enthalpies, and entropies for vapor-to-liquid transfers for water over a moderate temperature range to test the applicability of the van't Hoff equation are presented. The structural changes in the solvent phase causing the temperature dependence are also investigated.

The results of configurational-bias Monte Carlo simulations in the isobaric-isothermal ensemble for the aggregation behavior of 1-hexanol in dilute solutions in n-hexane are presented. The nonpolarizable TraPPE-UA (transferable potentials for phase equilibria-united atom) force field is used to carry out calculations for different concentrations and temperatures.

A TraPPE-UA force field is extended to linear and branched alkenes and alkylbenzenes by introduction of six new pseudo-atoms. These TraPPE-UA force field was also used to calculate the pressure-composition diagrams of two binary mixtures, and the results are found promising without requiring any special binary mixing parameters.

Research concerning the study of the efficiency and validity of the adiabatic nuclear and electronic sampling Monte Carlo algorithm (ANES-MC) is presented with reference to the Gibbs equation. The relevance of ANES-MC to force fields of water which are polarizable is discussed.

Research is presented concerning the study of vapor-liquid coexistence curves by the investigation of two fluctuating-charge and four dipole polarizable water force fields. Adiabatic nuclear and electronic sampling Monte Carlo simulations of Gibbs ensembles are used.

A transferable potentials for phase equilibria (TraPPE)-explicit hydrogen (EH) model for n-alkanes is developed and its force field is compared with the that of the TraPPE-united atom (UA), OPLS-UA and OPLS-AA models. Results indicate that explicit many-body dispersive terms have slight effect on the TraPPE force fields. Moreover, the TraPPE-EH force field outperforms the TraPPE-UA model for all multicomponent equilibria that was considered in the study.

A new generalization of the configurational-bias Monte Carlo method, which avoids problems usually found in a Boltzmann rejection method for sequetially generating bond bending and torsional angles, is shown. The transferable potentials for phase equilibria united-atom force field is extended to include Lennard-Jones interaction parameters for methine and quaternary carbon groups by fitting to critical temperatures and saturated liquid densities of branched alkanes.