Size dependence of lattice constants of semiconductor nanocrystals

We have theoretically examined the size dependence of the equilibrium lattice constant of nanocrystals of Si, GaAs and CdSe. While deviations from the bulk lattice constant are as large as 1-2% for unpassivated nanocrystals of Si, the deviations drop to ~ 0.3%-0.4% once the surfaces are passivated. Inspite of the fact that the average equilibrium bond-lengths are bulk-like, we find that the nearest-neighbor bond-length exhibits an unusual strain profile with bulk like bond-lengths in the core and shorter (~ 1%) bonds at the surface.