ST2 Model Research Articles

A Molecular Dynamics Study of Aqueous Solutions

Abstract The central force model for water has been employed in a molecular dynamics simulation of a 2.2 molal NaCl solution. The structural properties of the solution obtained are compared with results of previous simulations where the ST2 model of water was used. Preliminary results on the influence of the ions on the water molecule geometry in the hydration shells are reported. The spectral densities calculated from the hydrogen velocity autocorrelation functions by Fourier transformation indicate differences in the librational and vibrational frequencies between bulk water and hydration water of Na+ and Cl-.

A Molecular Dynamics Study of Aqueous Solutions. VIII. Improved Simulation and Structural Properties of a NH4Cl Solution

A molecular dynamics simulation of an aqueous ammonium chloride solution has been carried out at a mass density of 1.027 g/cm3, corresponding to a 2.2 m solution, and at a temperature of T = 301 K. The effective pair potentials are based on the ST2 model of water, a rigid tetra­hedral four point charge model of NH4 + and a single point charge model of Cl-. The calculated structural properties of this solution are discussed and compared with those obtained for alkali halide solutions. The first hydration shell of the ammonium ion contains on the average eight water molecules, it has a more complex structure than the hydration shells of cations with spherical symmetry. The static orientational order of water dipole moments indicate a structure breaking ability of NH4 +.

Inclusion of reaction fields in molecular dynamics. Application to liquid water

The influence of the inclusion of a reaction field on molecular dynamics simulations of liquid water (ST2 model) has been evaluated, both for a momentary and a delayed reaction field. The influence on radial distribution function and energy is not large, but the spatial dipolar correlation is changed considerably. Total dipole moment fluctuations are much enhanced by the reaction field. If the delay of the reaction field is not taken into account, the reaction field effects are overestimated.Dynamic properties are sensitive to the reaction field: the diffusion constant almost doubles and rotational correlation times decrease.Computer simulations were carried out over a total time of 55 ps with a cut-off radius of 0.578 nm and a time of 0.002 ps. The small cut-off and large time step do not influence the accuracy of statistical averages generated by the dynamics run.