Atomistic modeling of lattice relaxation in metallic nanocrystals

Surface relaxation in spherical nanocrystals, as studied in terms of the radial atomic displacement, was interpreted considering the effect of elastic anisotropy and variation in the coordination number. The proposed model captures the main phenomenology and keeps the number of adjustable parameters reasonable, however, it seems unable to represent the complexity of the lattice relaxation phenomena taking place in a metal nanoparticle. As with previous literature models of surface relaxation, the main effect observed on the powder diffraction pattern is a peak shift, with a limited but visible effect on the profile shape and width. Although approximate, the proposed model of radial atomic displacement, when applied to fit the powder pattern of a nanocrystal relaxed by molecular dynamics, allows for a much better match than any previous model. In particular, the anisotropy of the surface relaxation effect is at least qualitatively accounted for.

► Surface relaxation has a complex effect on local atomic arrangement in nanocrystals.
► Relaxation effects cannot be interpreted just in terms of radial atomic displacement.
► A model is proposed, based on coordination number and elastic anisotropy.
► The proposed model supports a correct interpretation of powder diffraction patterns.