  The morphological evolution of nanoporous gold is generally believed to be
governed by surface diffusion. This work specifically explores the dependence
of mass transport by surface diffusion on the curvature of a gold surface. The
surface diffusivity is estimated by molecular dynamics simulations for a
variety of surfaces of constant mean curvature, eliminating any chemical
potential gradients and allowing the possible dependence of the surface
diffusivity on mean curvature to be isolated. The apparent surface diffusivity
is found to have an activation energy of ~0.74 eV with a weak dependence on
curvature, but is consistent with the values reported in the literature. The
apparent concentration of mobile surface atoms is found to be highly variable,
having an Arrhenius dependence on temperature with an activation energy that
also has a weak curvature dependence. These activation energies depend on
curvature in such a way that the rate of mass transport by surface diffusion is
nearly independent of curvature, but with a higher activation energy of ~1.01
eV. The curvature dependencies of the apparent surface diffusivity and
concentration of mobile surface atoms is believed to be related to the expected
lifetime of a mobile surface atom, and has the practical consequence that a
simulation study that does not account for this finite lifetime could
underestimate the activation energy for mass transport via surface diffusion by
~0.27 eV.
