Surface atomic packing fraction as a figure of merit for the structural transition and the bulk-to-nano transformation of spherical FCC and BCC nanosolids

We report on the development of a simple and efficient method to predict the structural transition and the bulk-to-nano transformation of spherical FCC and BCC solid nanoparticles using the surface atomic packing fraction (g_s). For both structures, g_s ’s are maxima at radii equal to the nearest neighbor distances. These g_s values are smaller than the maximum values of their bulk counterparts. Compared to the bulk phase, the volume packing fraction (f) of a FCC nanoparticle decreases with size and approaches 0.810 at shells greater than 208. Our predictions show that bulk-to-nano transition starts at N~10⁴, in a good agreement with the relevant literature. The disturbing the spherical shape of small FCC nanoparticles is found to be easier than breaking them across {100} and {111} crystal planes. However, for BCC, small NPs are more difficult to break through {100} and {111} planes. The current results highlight possible mechanisms for controlling the physical properties of matter at the nanoscale through their morphological characteristics. This study demonstrates that the interplay between packing, structural transition and shape can be utilized to develop new nanomaterials with controlled properties.