*** Hybrid Computational Methods for Multiscale Modeling of Materials
May 12-14, 1999 at NIST Gaithersburg, Maryland. ***

Nearly Exact Solution for Coupled Continuum/MD Fluid Simulation

A general statistical approach is described to couple continuum with
molecular dynamics in fluid simulation. Arbitrary thermodynamic field
boundary conditions can be imposed on an MD system while minimally
disturbing the particle dynamics of the system. And by acting away
from the region of interest through a feedback control mechanism,
across a buffer zone where the disturbed dynamics are allowed to
relax, we can eliminate that disturbance entirely. The field
estimator, based on maximum likelihood inference, serves as the
detector of the control loop, which infers smooth instantaneous fields
from the particle data. The optimal particle controller, defined by an
implicit relation, can be proved mathematically to give the correct
distribution with least disturbance to the dynamics. A control
algorithm monitors the estimated current fields with the desired
fields at the boundary and modifies the behavior of the particle
controller far way, until they eventually agree. Using this method and
a continuum code under the Schwartz iterative domain-decomposition
formalism, it provides mutually consistent solution for most
steady-state problems where particles in the MD region has no way to
tell any difference with reality. Some illustrative results will be
discussed.