J. Knap and M. Ortiz
Physical Review Letters, 90, 226102 (2003).
We address the question of whether results obtained for small indenters scale
to indenter sizes in the experimental range. The quasicontinuum method is used
in order to extend the computational cell size to 2x2x1 um^3, nominally
containing of order 2.5x10^11 atoms, and in order to permit consideration
of indenter radii in the range 70-700 angstrom. The dislocation structures for
the large indenter are found to be less sharp and to extend over a larger
region than for the small indenter. In addition, the large-indenter
force-displacement curve differs from that corresponding to the small
indenter in one important respect, namely, the absence of force drops
during indentation, despite profuse dislocation activity. Based on these
observations, we conclude that the indenter force is not a reliable indicator
of the onset of dislocation activity and plastic deformation for indenter
sizes in the experimental range.