ST2 Model Of Water Research Articles

A Molecular Dynamics Study of the Structure of an Aqueous CsF Solution

Abstract A molecular dynamics simulation of a 2.2 molal aqueous CsF solution has been performed employing the ST2 water model. The basic periodic cube with a sidelength of 18.50 Å contained 200 water molecules, and 8 ions of each kind, corresponding to an experimental density of 1.26 g/cm3. The simulation extended over 6.5 ps with an average temperature of 307 K. The structure of the solution is discussed by means of radial distribution functions and the orientation of the water molecules. The computed hydration numbers in the first shell of Cs+ and F- are 7.9 and 6.8, respectively; the corresponding first hydration shell radii are 3.22 A and 2.64 A, respectively. Values for the hydration shell energies and the heat of solution have been calculated.

Structural Properties of an Aqueous LiI Solution Derived from a Molecular Dynamics Simulation

In the molecular dynamics simulation of the aqueous LiI solution the ST2 water model was employed and the ions were described as Lennard-Jones spheres with an elementary charge at the center. The basic periodic cube contained 200 water molecules and 8 ions of each kind equivalent to a 2.2 molal solution. The simulation extended over 10 ps with an average temperature of 305 K. The structure is discussed by means of ion-water, ion-ion and water-water radial pair distribution functions and the orientation of the water molecules. Potential energy relationships are reported and the heat of solution has been calculated and found in agreement with experimental values.

ChemInform Abstract: THE STRUCTURE OF AN AQUEOUS AMMONIUM CHLORIDE SOLUTION

AbstractDie Ergebnisse von Röntgenstreuungsmessungen an einer 2 molalen NH4Cl‐Lösung werden mit aus der Molekulardynamik auf der Basis des Modells ST2 für Wasser abgeleiteten Vorstellungen verglichen.

The structure of an aqueous ammonium chloride solution

X-ray measurements have been performed on a 2 molal NH4 Cl solution at 25 °C. The scattering data have been evaluated with the first neighbor model (FNM). These results are compared with molecular dynamics (MD) simulations where the ST2 model for water is employed. The NH4+ is described by a rigid tetrahedron with point charges at the positions of the hydrogen atoms and the Cl− by a Lennard-Jones sphere with an elementary charge at the center. Good agrement has been found between the measurements and the simulation. Contrary to previous results the nearest neighbor distance for NH4+–water is found to be significantly different from the one for water–water. The structure of the solvent described by the nearest neighbor distance and its root mean square deviation is in the limits of error the same as in pure water and significantly different from the solvent structure in alkali halide solutions.

A molecular dynamics study of an aqueous NaCl-solution

In this molecular dynamics study on an aqueous NaCl solution a central force model for water was employed. The pair potentials between oxygen-oxygen, oxygen-hydrogen and hydrogen-hydrogen were taken from the latest version of the central force water given by Stillinger and Rahman [1]. The ion—oxygen and ion—hydrogen pair potentials were adjusted to ab initio calculations of Kistenmacher, Popkie and Clementi [2]. The basic periodic box with a sidelength of 18.42 Å contained 200 oxygen atoms, 400 hydrogen atoms, 8 sodium and 8 chloride ions equivalent to a 2.2 molal solution. The stimulation was extended over 3500 time steps of 4 × 10 −16 seconds to a total time of 1.4 picoseconds. Structural properties are obtained and discussed, e.g. the different radial distribution functions, the orientation of the water molecules in the hydration shell of the ions and the influence of the ions on water geometry. These properties are compared to those of an earlier simulation of an aqueous NaCl solution with the rigid ST2-water model. Especially the double peak in the range of the first maximum of the experimental ▪ Fig. 1. Comparison of the structure function from an X-ray investigation of a 2 molal NaCl solution (dotted) [4] with the structure functions derived from MD simulations of a 2.2 molal NaCl solution with CF-water (Full) and ST2 water (dashed) [3]. ▪ Fig 2. Normalized velocity autocorrelation function for all hydrogens in a 2.2. molal NaCl solution from a simulation with CF water. structure the velocity autocorrelation function of the hydrogens (Fig. 2) hindered translational, librational and vibrational frequencies are derived and differences in these frequencies between the hydration water of the ions and bulk water are discussed.

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 +.