Neste trabalho, propriedades de hidratação do íon Al3+ são investigadas por simulações mecânico-estatísticas de Monte Carlo no ensemble NpT a 298,15 K e 1 atm usando um modelo de potencial efetivo de pares íon-água cujos parâmetros foram desenvolvidos por meio de busca empírica no espaço de fase configuracional durante o curso das simulações para reproduzir dados experimentais da estrutura da primeira camada de hidratação. Resultados estruturais obtidos a partir das simulações para números de coordenação e distâncias íon-oxigênio da água, correspondentes às camadas de hidratação primeira e segunda, estão em muito bom acordo com dados experimentais. A entalpia de hidratação predita a partir deste modelo também está em muito bom acordo com resultados experimentais e é bastante similar ao resultado obtido por Wasserman et al. a partir do modelo de íon hidratado. Contribuições de muitos corpos investigadas para um cluster [Al(H2O)6]3+ usando a teoria do funcional de densidade em cálculos mecânico-quânticos de primeiros princípios fornecem suporte à efetividade do potencial de pares íon-água desenvolvido quanto aos efeitos de muitos corpos incorporado nos parâmetros ajustados.

In this work, hydration properties of Al3+ ion are investigated by statistical mechanics Monte Carlo simulations in the NpT ensemble at 298.15 K and 1 atm using an effective ion-water potential model whose parameters were developed through empirical search in configurational energy space during the course of simulations to fitting structural experimental data of the first hydration shell. Computed structural results for coordination numbers and ion-water oxygen distances for both first and second coordination shells are obtained in very good agreement with experimental observations. The hydration enthalpy predicted from this simple model is also in very good agreement with experimental values and it is quite similar to the one obtained by Wasserman et al. from the hydrated ion model. Many-body contributions investigated for an [Al(H2O)6]3+ cluster using the density functional theory in ab initio quantum mechanical calculations provide support to the effectiveness of the ion-water pair potential developed concerning many-body effects of water molecules around the ion incorporated in the fitted parameters.

Thermodynamic properties and radial distribution functions for liquid chloroform were calculated using the Monte Carlo method implemented with Metropolis algorithm in the NpT ensemble at 298 K and 1 atm. A five site model was developed to represent the chloroform molecules. A force field composed by Lennard-Jones and Coulomb potential functions was used to calculate the intermolecular energy. The partial charges needed to represent the Coulombic interactions were obtained from quantum chemical ab initio calculations. The Lennard-Jones parameters were adjusted to reproduce experimental values for density and enthalpy of vaporization for pure liquid. All thermodynamic results are in excelent agreement with experimental data. The correlation functions calculated are in good accordance with theoretical results avaliable in the literature. The free energy for solvating one chloroform molecule into its own liquid at 298 K and 1 atm was computed as an additional test of the potential model. The result obtained compares well with the experimental value. The medium effects on cis/trans convertion of a hypotetical solute in water TIP4P and chloroform solvents were also accomplished. The results obtained from this investigation are in agreement with estimates of the continuous theory of solvation.

Statistical mechanics Monte Carlo simulation is reviewed as a formalism to study thermodynamic properties of liquids. Considering the importance of free energy changes in chemical processes, the thermodynamic perturbation theory implemented in the Monte Carlo method is discussed. The representation of molecular interaction by the Lennard-Jones and Coulomb potential functions is also discussed. Charges derived from quantum molecular electrostatic potential are also discussed as an useful methodology to generate an adequate set of partial charges to be used in liquid simulation.