To the editor —

In the recent News and Views article “Less is more” by E. Ma, T. D. Shen and X. L. Wu1, the authors have incorrectly interpreted our molecular dynamics simulation results. In order to support their belief that the propagation of dislocations is easier than the nucleation of dislocations, the authors refer to our recent molecular dynamics simulation results2, stating “In fact, their movement is easier under applied stresses than the generation of new dislocations from grain boundaries.”

Our paper does not support this statement. On the contrary, our simulations and experiments3,4 suggest the importance of dislocation propagation. Reporting the details of the nucleation and propagation obtained from molecular dynamics, we demonstrated that dislocation propagation is hindered by the ledges in the grain boundaries, and that propagation can be as important as nucleation. Our paper2 ends with the sentence “The present paper demonstrates that dislocation propagation can play as important a role as dislocation nucleation and that this should be taken into account in any continuum model for the rate-controlling mechanism of dislocation activity in nanocrystalline materials”.

The opinion adopted by the authors in their News and Views piece, that nucleation is the rate-limiting process, is an extremely strong statement that is still not supported by experiments. Moreover, their statement seems not to be in accordance with discussions in the authors' own experimental papers5,6.

At the current level of understanding, the rate-limiting process for plastic deformation is still an open question. Suggestions from molecular dynamics simulations such as those presented in ref. 2 should motivate further in-depth experimental research exploring the details of the deformation mechanism aiming to determine the character of the rate-limiting processes in grain-boundary-dominated structures, an input of utmost importance for developing reliable mesoscopic models.