K. Heinzinger

An improved potential for non-rigid water molecules in the liquid phase

Abstract A modification of the central-force model for liquid water is proposed; a spectroscopic potential is adapted to describe the intramolecular interactions. Gas—liquid shifts of internal vibrational frequencies obtained from MD simulations are in good agreement with available spectroscopic data.

Molecular dynamics study of high-density liquid water using a modified central-force potential

Abstract Molecular dynamics simulations of liquid water at densities of 0.9718 and 1.346 g/cm3, and at temperatures of 63 and 77°C have been performed employing a modified version of the central-force model of water. The structural changes observed are in reasonably good agreement with recent high-pressure neutron scattering studies. The self-diffusion coefficient has been found to decrease by ≈ 35% on compression. The OH stretching frequency underwent a shift of 10 cm-1 in the direction of lower frequencies and was accompanied by an increase in the average OH bond length.

Molecular dynamics simulations of water-methanol mixtures

Abstract Molecular dynamics simulations of two water-methanol mixtures with methanol mole fractions of 0.1 and 0.9 at room temperature have been performed. The interaction potentials are based on flexible three-site models for water and methanol. The structural changes relative to the pure solvents are demonstrated with the help of radial distribution functions and the geometrical arrangement of nearest-neighbor molecules. Differences in thermodynamic properties and in hydrogen bonding between the two mixtures and relative to the pure liquids are discussed.

A molecular dynamics study of water between Lennard-Jones walls

Abstract An MD simulation of 216 ST2 water molecules between 12-6 Lennard-Jones walls has been performed which extend over 20 ps at an average temperature of 287 K. The oxygen atom density profile is reported the influence of the walls on the orientation of the water molecules on the self-diffusion coefficient have been investigated The results are compared with those from MC and MD simulations of similar systems.

Molecular dynamics simulation of a water/metal interface

First results of a molecular dynamics study of a water/metal interface, lasting 3.3 ps at an average temperature of 294 K, are reported. The basic periodic box contains 216 water molecules and a crystal slab of 550 platinum atoms with (100) surface planes. A combination of a Lennard-Jones potential between centers of mass and Coulomb potential arising from dielectric interactions of the water charge distribution with the metal is employed for the water-wall interaction, the ST2 model for the water-water, and nearest-neighbour harmonic potential for the platinum-platinum interactions. Considerable adsorption at the interface together with a drastic change of the water structure is observed.

Molecular dynamics simulation of a chloride ion in water under the influence of an external electric field

Molecular dynamics simulations were performed for one chloride ion in 213 water molecules under various applied external electrical fields. The field strength varied from 0.5–2⋅1010 V/m. The structure of the solution is described by various radial distribution functions, hydrogen bond statistics, and the deviation from tetrahedrality. The selfdiffusion coefficients and the spectral densities of the hindered translational motions of the water molecules have been calculated from the velocity autocorrelation functions. The dependence of these properties on the strength of the external electrical field is discussed.

Molecular dynamics investigation of the inter- and intramolecular motions in liquid methanol and methanol-water mixtures

Molecular dynamics computer simulations were performed at room temperature and selected density on pure liquid methanol and water, and on methanol-water mixtures with methanol mole fractions of 0·1...

A molecular dynamics study of the translational and rotational motions in an aqueous LiI solution

The spectral densities of the hindered translations and librations for the ions and the water molecules in a 2.2 m LiI solution have been derived from an MD simulation with the ST2 model for water. The reorientational times of the dipole moment vector, the intramolecular proton–proton vector as well as the ion–oxygen and ion–hydrogen vectors are also reported. The separate calculation of various properties for the three water subsystems—hydration water of the cation, of the anion and bulk water—contributes significantly to the understanding of macroscopically measured quantities on a molecular level.

Structure and dynamics of water and hydrated ions near platinum and mercury surfaces as studied by MD simulations

Results of various MD simulations of pure water and those with either an additional lithium or iodide ion near a Pt(100), a rigid and a liquid mercury surface are reported. The potentials describing the interactions with the metal surfaces are based on ab initio calculations of a water molecule or an ion and metal clusters of different sizes. The flexible BJH and the rigid TIP4P models for water are employed and the ion-water interactions are also derived from ab initio calculations. The structure at the interfaces for pure water at the three different surfaces is described by oxygen, hydrogen and mercury atom density profiles. The effect of all three metal surfaces on the structure of the hydration shells of the lithium and the iodide ion are discussed in detail and the free energies are reported as a function of distance from the rigid mercury surface. The spectral densities of the hindered translational motions of both ions parallel and perpendicular to the Pt(100) and the liquid mercury surface are presented.

Quantum chemical study of the adsorption of an H2O molecule on an uncharged mercury surface

Despite the fact that attempts were made to describe the interaction of a single H2O molecule with a mercury surface, using both semi-empirical and ab initio quantum chemical calculations, reliable microscopic information on the Hg | H2O interface is still lacking. In this work, non-empirical quantum chemical calculations were carried out to study water molecule adsorption on an uncharged mercury electrode. The mercury surface was modelled by a cluster Hgn, with n = 6, 7. The effect of electronic correlation plays an important role. An “on-top” position of the H2O molecule with the dipole moment pointing away from the surface reveals an adsorption energy minimum (ΔEads) of −38.5 kJ mol−1. The dipole reorientation energy was estimated to be 21.8 kJ mol−1. According to our results, the dependence of ΔEads on the tilt angle has no limit. Analysis of the chemical binding between the cluster and the H2O molecule shows the electrostatic nature of the binding. The mean field approximation was applied to describe the interaction between the adsorbed H2O molecules in a monolayer. The results were in agreement with experimental data.