  We used density functional theory (DFT) calculations to investigate the
physical origin of the mechano-chemical response of materials interfaces. Our
results show that the mechano-chemical response can be decomposed into the
contribution from the interface itself (deformation of interfacial bonds) and a
contribution from the underlying solid. The relative contributions depend on
the stiffness of these regions and the contact geometry, which affects the
stress distribution within the bulk region. We demonstrate that, contrary to
what is commonly assumed, the contribution to the activation volume from the
elastic deformation of the surrounding bulk is significant and, in some case,
may be dominant. We also show that the activation volume and the
mechanochemical response of interfaces should be finite due to the effects on
the stiffness and stress distribution within the near-surface bulk region. Our
results indicate that the large range of activation volumes measured in the
previous experiments even for the same material system might originate from the
different degrees of contributions probed from the bulk vs. interface.
