  An atomistic model based on the Keating potential and the conjugate gradient
method are used for simulation of the strain fields for single Ge/Si quantum
dots. Calculations are performed in the cluster approximation using clusters
containing about three million atoms belonging to 150 coordination spheres. The
spatial distributions of the strain energy density and electron potential
energy are calculated for different valleys forming the bottom of the silicon
conduction band. It is shown that the strain field in silicon decreases
sufficiently rapidly with distance from the center of the quantum dot, so the
influence of the cluster boundary is observed only for very large quantum dots.
