  We present quantum-based simulations of single grain boundary reflectivity of
electrons in metals, Cu and Ag. We examine twin and non-twin grain boundaries
using non-equilibrium Green's function and first principles methods. We also
investigate the mechanism of reflectivity in grain boundaries by modeling
atomic vacancies, disorder, and orientation and find that the change in grain
orientation and disorder in the boundary itself both contribute significantly
to reflectivity. We find that grain boundary reflectivity may vary widely
depending on the grain boundary structure consistent with experimental results.
Finally, we examine the reflectivity from multiple grain boundaries and find
that grain boundary reflectivity may depend on neighboring grain boundaries.
This study based on detailed numerical techniques reveals some potential
limitations in the independent grain boundary assumptions of the
Mayadas-Shatzkes model.
