  Diamond-based coatings are employed in several technological applications,
for their outstanding mechanical properties, biocompatibility, and chemical
stability. Of significant relevance is the interface with silicon oxide, where
phenomena of adhesion, friction, and wear can affect drastically the
performance of the coating. Here we monitor such phenomena in real-time by
performing massive ab initio molecular dynamics simulations in tribological
conditions. We take into account many relevant factors that can play a role,
i.e. the diamond surface orientation and reconstruction, silanol density, as
well as, the type and concentration of passivating species. The large systems
size and the long simulations time, put our work at the frontier of what can be
currently done with fully ab initio molecular dynamics. The results of our work
point to full hydrogenation as an effective way to reduce both friction and
wear for all diamond surfaces, while graphitization is competitive only on the
(111) surface. Overall we expect that our observations will be useful to
improve technological applications where the silica-diamond interface plays a
key role. Moreover, we demonstrate that realistic and accurate in silico
experiments are feasible nowadays exploiting HPC resources and HPC optimized
software, paving the way to a more general understanding of the relationship
between surface chemistry and nanoscale-tribology.
