A broad class of "local response" theories seeks to predict morphology evolution during energetic particle irradiation in terms of average surface height response to individual impacts-an approach that has been generalized by the crater function formalism of Norris et al. [J. Phys.: Condens. Matter 21, 224017 (2009); Nat. Commun. 2, 276 (2011) ]. Keeping only the terms in the crater function formalism associated with the response of a flat surface has facilitated the use of molecular dynamics

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... mulations of individual ion impacts to predict the stability or instability of a flat surface to ion bombardment. Here we report a sensitive experimental test of this truncated crater function theory that is independent of any a priori knowledge of the crater function itself. Existing measurements for 1 keV Ar + /Si and Kr + /Ge are inconsistent with the predictions of truncated crater function theory, for any conceivable crater function, at high bombardment angles. The failure of the theory suggests that the prediction of surface evolution from simulations of single-ion impacts will be more challenging than had been assumed.