2 research outputs found
ChIMES: A Force Matched Potential with Explicit Three-Body Interactions for Molten Carbon
We present a new
force field and development scheme for atomistic
simulations of materials under extreme conditions. These models, which
explicitly include two- and three-body interactions, are generated
by fitting linear combinations of Chebyshev polynomials through force
matching to trajectories from Kohn–Sham density functional
theory (DFT). We apply our method to liquid carbon near the diamond/graphite/liquid
triple point and at higher densities and temperatures, where metallization
and many-body effects may be substantial. We show that explicit inclusion
of three-body interaction terms allows our model to yield improved
descriptions of both dynamic and structural properties over previous
empirical potential efforts, while exhibiting transferability to nearby
state points. The simplicity of our functional form and subsequent
efficiency of parameter determination allow for extension of DFT to
experimental time and length scales while retaining most of its accuracy
Probing Additive Loading in the Lamellar Phase of a Nonionic Surfactant: Gibbs Ensemble Monte Carlo Simulations Using the SDK Force Field
Understanding
solute uptake into soft microstructured materials,
such as bilayers and worm-like and spherical micelles, is of interest
in the pharmaceutical, agricultural, and personal care industries.
To obtain molecular-level insight on the effects of solutes loading
into a lamellar phase, we utilize the Shinoda–Devane–Klein
(SDK) coarse-grained force field in conjunction with configurational-bias
Monte Carlo simulations in the osmotic Gibbs ensemble. The lamellar
phase is comprised of a bilayer formed by triethylene glycol mono-<i>n</i>-decyl ether (C10E3) surfactants surrounded by water with
a 50:50 surfactant/water weight ratio. We study both the unary adsorption
isotherm and the effects on bilayer structure and stability caused
by <i>n</i>-nonane, 1-hexanol, and ethyl butyrate at several
different reduced reservoir pressures. The nonpolar <i>n</i>-nonane molecules load near the center of the bilayer. In contrast,
the polar 1-hexanol and ethyl butyrate molecules both load with their
polar bead close to the surfactant head groups. Near the center of
the bilayer, none of the solute molecules exhibits a significant orientational
preference. Solute molecules adsorbed near the polar groups of the
surfactant chains show a preference for orientations perpendicular
to the interface, and this alignment with the long axis of the surfactant
molecules is most pronounced for 1-hexanol. Loading of <i>n</i>-nonane leads to an increase of the bilayer thickness, but does not
affect the surface area per surfactant. Loading of polar additives
leads to both lateral and transverse swelling. The reduced Henry’s
law constants of adsorption (expressed as a molar ratio of additive
to surfactant per reduced pressure) are 0.23, 1.4, and 14 for <i>n</i>-nonane, 1-hexanol, and ethyl butyrate, respectively, and
it appears that the SDK force field significantly overestimates the
ethyl butyrate–surfactant interactions