  Noble metal nanostructures are ubiquitous elements in nano-optics, supporting
plasmon modes that can focus light down to length scales commensurate with
nonlocal effects associated with quantum confinement and spatial dispersion in
the underlying electron gas. Nonlocal effects are naturally more prominent for
crystalline noble metals, which potentially offer lower intrinsic loss than
their amorphous counterparts, and with particular crystal facets giving rise to
distinct electronic surface states. Here, we employ a quantum-mechanical model
to describe nonclassical effects impacting the optical response of crystalline
noble-metal films and demonstrate that these can be well-captured using a set
of surface-response functions known as Feibelman $d$-parameters. In particular,
we characterize the $d$-parameters associated with the (111) and (100) crystal
facets of gold, silver, and copper, emphasizing the importance of surface
effects arising due to electron wave function spill-out and the
surface-projected band gap emerging from atomic-layer corrugation. We then show
that the extracted $d$-parameters can be straightforwardly applied to describe
the optical response of various nanoscale metal morphologies of interest,
including metallic ultra-thin films, graphene-metal heterostructures hosting
extremely confined acoustic graphene plasmons, and crystallographic faceted
metallic nanoparticles supporting localized surface plasmons. The tabulated
$d$-parameters reported here can circumvent computationally expensive
first-principles atomistic simulations to describe microscopic nonlocal effects
in the optical response of mesoscopic crystalline metal surfaces, which are
becoming widely available with increasing control over morphology down to
atomic length scales for state-of-the-art experiments in nano-optics.

Mesoscale and Nanoscale Physics;Materials Science;Optics;Quantum Physics