3 research outputs found
Using Force Matching To Determine Reactive Force Fields for Water under Extreme Thermodynamic Conditions
We present a method for the creation
of classical force fields
for water under dissociative thermodynamic conditions by force matching
to molecular dynamics trajectories from Kohn–Sham density functional
theory (DFT). We apply our method to liquid water under dissociative
conditions, where molecular lifetimes are less than 1 ps, and superionic
water, where hydrogen ions diffuse at liquid-like rates through an
oxygen lattice. We find that, in general, our new models are capable
of accurately reproducing the structural and dynamic properties computed
from DFT, as well as the molecular concentrations and lifetimes. Overall,
our force-matching approach presents a relatively simple way to create
classical reactive force fields for a single thermodynamic state point
that largely retains the accuracy of DFT while having the potential
to access experimental time and length scales
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
Generating Converged Accurate Free Energy Surfaces for Chemical Reactions with a Force-Matched Semiempirical Model
We demonstrate the
capability of creating robust density functional
tight binding (DFTB) models for chemical reactivity in prebiotic mixtures
through force matching to short time scale quantum free energy estimates.
Molecular dynamics using density functional theory (DFT) is a highly
accurate approach to generate free energy surfaces for chemical reactions,
but the extreme computational cost often limits the time scales and
range of thermodynamic states that can feasibly be studied. In contrast,
DFTB is a semiempirical quantum method that affords up to a thousandfold
reduction in cost and can recover DFT-level accuracy. Here, we show
that a force-matched DFTB model for aqueous glycine condensation reactions
yields free energy surfaces that are consistent with experimental
observations of reaction energetics. Convergence analysis reveals
that multiple nanoseconds of combined trajectory are needed to reach
a steady-fluctuating free energy estimate for glycine condensation.
Predictive accuracy of force-matched DFTB is demonstrated by direct
comparison to DFT, with the two approaches yielding surfaces with
large regions that differ by only a few kcal mol<sup>–1</sup>