  Strain has a crucial effect on the optical and electronic properties of
nanostructures. We calculate the atomistic strain distribution in silicon
nanocrystals up to a diameter of 3.2 nm embedded in an amorphous silicon
dioxide matrix. A seemingly conflicting picture arises when the strain field is
expressed in terms of bond lengths versus volumetric strain. The strain profile
in either case shows uniform behavior in the core, however it becomes
nonuniform within 2-3 \AA distance to the nanocrystal surface: tensile for bond
lengths whereas compressive for volumetric strain. We reconsile their
coexistence by an atomistic strain analysis.
