A. H. Narten

Bio: A. H. Narten is an academic researcher. The author has contributed to research in topics: Electron density & Scattering. The author has an hindex of 1, co-authored 1 publications receiving 605 citations.

Liquid Water: Molecular Correlation Functions from X‐Ray Diffraction

Abstract: For nearly spherical molecules the x‐ray scattering from liquids yields structure and correlation functions for molecular scattering centers. The distribution of electron density in a water molecule is very nearly spherical, and orientational correlation between molecules in the liquid is not ``seen'' by x rays. Structure and correlation functions for molecular scattering centers are derived from x‐ray data on water and tabulated. They provide a sensitive test for future work on a molecular theory of liquid water.

Comparison of simple potential functions for simulating liquid water

Abstract: Classical Monte Carlo simulations have been carried out for liquid water in the NPT ensemble at 25 °C and 1 atm using six of the simpler intermolecular potential functions for the water dimer: Bernal–Fowler (BF), SPC, ST2, TIPS2, TIP3P, and TIP4P. Comparisons are made with experimental thermodynamic and structural data including the recent neutron diffraction results of Thiessen and Narten. The computed densities and potential energies are in reasonable accord with experiment except for the original BF model, which yields an 18% overestimate of the density and poor structural results. The TIPS2 and TIP4P potentials yield oxygen–oxygen partial structure functions in good agreement with the neutron diffraction results. The accord with the experimental OH and HH partial structure functions is poorer; however, the computed results for these functions are similar for all the potential functions. Consequently, the discrepancy may be due to the correction terms needed in processing the neutron data or to an effect uniformly neglected in the computations. Comparisons are also made for self‐diffusion coefficients obtained from molecular dynamics simulations. Overall, the SPC, ST2, TIPS2, and TIP4P models give reasonable structural and thermodynamic descriptions of liquid water and they should be useful in simulations of aqueous solutions. The simplicity of the SPC, TIPS2, and TIP4P functions is also attractive from a computational standpoint.

Interaction Models for Water in Relation to Protein Hydration

Abstract: For molecular dynamics simulations of hydrated proteins a simple yet reliable model for the intermolecular potential for water is required. Such a model must be an effective pair potential valid for liquid densities that takes average many-body interactions into account. We have developed a three-point charge model (on hydrogen and oxygen positions) with a Lennard-Jones 6–12 potential on the oxygen positions only. Parameters for the model were determined from 12 molecular dynamics runs covering the two-dimensional parameter space of charge and oxygen repulsion. Both potential energy and pressure were required to coincide with experimental values. The model has very satisfactory properties, is easily incorporated into protein-water potentials, and requires only 0.25 sec computertime per dynamics step (for 216 molecules) on a CRAY-1 computer.

Structure and Dynamics of the TIP3P, SPC, and SPC/E Water Models at 298 K

Abstract: Molecular dynamics simulations of five water models, the TIP3P (original and modified), SPC (original and refined), and SPC/E (original), were performed using the CHARMM molecular mechanics program. All simulations were carried out in the microcanonical NVE ensemble, using 901 water molecules in a cubic simulation cell furnished with periodic boundary conditions at 298 K. The SHAKE algorithm was used to keep water molecules rigid. Nanosecond trajectories were calculated with all water models for high statistical accuracy. The characteristic self-diffusion coefficients D and radial distribution functions, gOO, gOH, and gHH for all five water models were determined and compared to experimental data. The effects of velocity rescaling on the self-diffusion coefficient D were examined. All these empirical water models used in this study are similar by having three interaction sites, but the small differences in their pair potentials composed of Lennard-Jones (LJ) and Coulombic terms give significant difference...

Improved simulation of liquid water by molecular dynamics

Abstract: Molecular dynamics calculations on a classical model for liquid water have been carried out at mass density 1 g/cm3 and at four temperatures. The effective pair potential employed is based on a four‐charge model for each molecule and represents a modification of the prior ``BNS'' interaction. Results for molecular structure and thermodynamic properties indicate that the modification improves the fidelity of the molecular dynamics simulation. In particular, the present version leads to a density maximum near 27°C for the liquid in coexistence with its vapor and to molecular distribution functions in better agreement with x‐ray scattering experiments.