Effective pair‐potential models, parametrized to the properties of the pure liquids, have been used in molecular‐dynamics simulations of aqueous (binary) mixtures containing methanol, ammonia, or acetone. Results are reported for thermodynamic and structural properties, self‐diffusion coefficients, and reorientational correlation times. There is fair agreement with a wide variety of experimental data. The pattern of hydrogen bonding and the distribution of hydrogen‐bond lifetimes in the simulated mixtures have been investigated. The observed anomalous behavior of methanol and acetone solutions appears to be related to specific features of the hydrogen bonding—namely, the ability of these molecules to exhibit enhanced acceptor character. As a consequence of the assumed intermolecular potentials, the balance between the competing effects of hydrophobic hydration of methyl groups and hydrogen bonding to oxygen atoms is tipped towards the latter. A number of interesting structural effects have been noted. In particular, the distribution function g(R) for water oxygen atoms sharpens appreciably on addition of the second component. The structure of the water–ammonia system is discussed in detail. There is good accord with available x‐ray data at low concentration, but there are no measurements available to test the predictions at high concentration.

The dynamics of rigid polyatomic systems, either molecules or rigid portions of large molecules, is described by cartesian equations of motion for its atoms. In comparison with the original version of the method of constraints [1], the present approach has more general applicability, on account of a proper choice of holonomic constraints. Moreover, it always leads to a more efficient molecular dynamics simulation of polyatomic molecules. The dynamics of a rigid unit is provided by the motion of a ‘basic’ subset of atoms: two for a linear molecule, three for a planar one, four for a tridimensional one. Explicit cartesian equations of motion of the ‘basic’ atoms are derived from first principles. Verlet algorithm is shown to be particularly advantageous in their numerical integration. Illustrations are given for various molecular geometries, i.e. liquid CS2, benzene and CCl4. © 1982 Taylor & Francis, Ltd.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

The reaction rate and mechanism of the interconversion between a contact ion pair and solvent separated ion pair in model polar solvents is investigated by molecular dynamics (MD) simulation. The full rate constant for the model reaction is estimated from the product of the transition state theory (TST) rate constant, determined from the potential of mean force between the ions in an equilibrium solvent, and the transmission coefficient, which depends on the details of the dynamics. The collective character of the solvent motion in the reaction barrier crossing is examined in some detail, and the important role of solvent dynamics in causing the reaction rate to markedly deviate from the TST rate is discussed. The MD results are compared with the predictions of Kramers and Grote–Hynes theories.