The size-dependent elastic response of nanomaterials and nanostructures with a large surface-to-volume ratio has attracted increasing attention. For example, in the order of tenfold stiffening has been reported for nanoporous gold (NPG) as the ligament size is decreased [1,2]. The local elasticity of the surface, expressed in terms of the surface excess elastic constants has been proposed as a key factor regarding this considerable size effect – and in fact, for NPG the contribution of surface excess
elasticity to the effective elastic response has been experimentally verified . However, quantitative prediction of the influence of surface excess elasticity remains a challenging task, which is addressed in this contribution.
Density Functional Theory (DFT) simulations are employed to compute the surface excess elastic constants for selected low-index metallic surfaces, such as the (111) and (001) surfaces of gold. As a nanostructure is deformed, the effective stiffness arises from the interplay between bulk elasticity
and the contribution of the surface. Combination of the DFT parameters with a continuum description of a circular nanowire subjected to axial tension, bending, or torsion allows to assess the relative stiffness change as a function of the nanowire diameter.
Positive-valued surface excess elastic constants for gold indeed imply a stiffening effect of the surfaces. However, even for nanowire diameters as small as 10 nm, the relative change in stiffness only amounts to a few percent – implying that surface excess elasticity does not exclusively explain the experimentally observed size effect.
 A. Mathur, J. Erlebacher, Appl. Phys. Lett. 90, 061910 (2007).
 N. Mameka, K. Wang, J. Markmann, E. T. Lilleodden, J. Weissmüller, Mater. Res. Lett. 4, 27 (2016).
 N. Mameka, J. Markmann, H.-J. Jin, J. Weissmüller, Acta Materialia 76, 272 (2014).