  We study theoretically the electron states in a system of two vertically
stacked quantum dots. We investigate the influence of the geometrical symmetry
breaking (caused by the displacement as well as the ellipticity of the dots) on
the electron states. Our modeling is based on the 8-band kp method. We show
that the absence of axial symmetry of the system leads to a coupling of the s
state from one dot with the p and d states from the other. Our findings
indicate, that this coupling can produce a strong energy splitting at resonance
(on the order of several meV) in the case of closely spaced quantum dots.
Furthermore, we show that in the presence of a piezoelectric field, the
direction of the displacement plays an important role in the character of the
coupling.
