We perform atomistic simulations for the structure and elastic properties of nanocrystalline Cu. We observe softening at small grain sizes, in analogy with the reverse Hall‐Petch effect for plastic deformations in nanocrystalline metals. The decrease of elastic constants is explained by the increase of the fraction of grain boundary atoms for smaller grains. By decomposing the energy into contributions from atoms in the bulk of grains and at interfaces, we derive simple scaling relations for various properties as a function of the average grain size. These theoretical predictions fit very well the simulation data, as well as published data for nanocrystalline diamond. This suggests that softening at small grain sizes is a general nanoscale effect. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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