Georgia Institute of Technology College of Sciences

Multiscale numerical methods seek to compute approximate solutions to physical problems at a reduced computational cost compared to direct numerical simulations. This talk will cover two methods which have a fine scale atomistic model that couples to a coarse scale continuum approximation. The quasicontinuum method directly couples a continuum approximation to an atomistic model to create a coherent model for computing deformed configurations of crystalline lattices at zero temperature. The details of the interface between these two models greatly affects the model properties, and we will discuss the interface consistency, material stability, and error for energy-based and force-based quasicontinuum variants along with the implications for algorithm selection. In the case of crystalline lattices at zero temperature, the constitutive law between stress and strain is computed using the Cauchy-Born rule (the lattice deformation is locally linear and equal to the gradient). For the case of complex fluids, computing the stress-strain relation using a molecular model is more challenging since imposing a strain requires forcing the fluid out of equilibrium, the subject of nonequilibrium molecular dynamics. I will describe the derivation of a stochastic model for the simulation of a molecular system at a given strain rate and temperature.