**Multiscale reactive molecular dynamics**

C Knight and GE Lindberg and GA Voth, JOURNAL OF CHEMICAL PHYSICS, 137, 22A525 (2012).

DOI: 10.1063/1.4743958

Many processes important to chemistry, materials science, and biology
cannot be described without considering electronic and nuclear-level
dynamics and their coupling to slower, cooperative motions of the
system. These inherently multiscale problems require computationally
efficient and accurate methods to converge statistical properties. In
this paper, a method is presented that uses data directly from condensed
phase ab initio simulations to develop reactive molecular dynamics
models that do not require predefined empirical functions. Instead, the
interactions used in the reactive model are expressed as linear
combinations of interpolating functions that are optimized by using a
linear least-squares algorithm. One notable benefit of the procedure
outlined here is the capability to minimize the number of parameters
requiring nonlinear optimization. The method presented can be generally
applied to multiscale problems and is demonstrated by generating
reactive models for the hydrated excess proton and hydroxide ion based
directly on condensed phase ab initio molecular dynamics simulations.
The resulting models faithfully reproduce the water-ion structural
properties and diffusion constants from the ab initio simulations.
Additionally, the free energy profiles for proton transfer, which is
sensitive to the structural diffusion of both ions in water, are
reproduced. The high fidelity of these models to ab initio simulations
will permit accurate modeling of general chemical reactions in condensed
phase systems with computational efficiency orders of magnitudes greater
than currently possible with ab initio simulation methods, thus
facilitating a proper statistical sampling of the coupling to slow,
large-scale motions of the system. (C) 2012 American Institute of
Physics. **http://dx.doi.org/10.1063/1.4743958**

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