  The possibility of controlling the optical transition probability between
neighbouring silicon nanoclusters (Si-NCs) constitutes nowadays an attractive
prospect in nanophotonics and photovoltaics. In this work, by means of
theoretical ab-initio calculations we investigate the effect of strain on the
opto-electronic properties of Si-NCs pairs. We consider two sources of strain:
the strain induced by an embedding SiO2 matrix, and the strain generated by
mutual NC-NC forces occurring at small distances. Independently on its source,
we observe a fundamental impact of the strain on the orbitals localization and,
as a consequence, on the transition probability between energy states,
belonging or not to the same NC. The resulting picture allots to the structural
strain a fundamental role in the NC-NC interaction mechanisms, suggesting the
possibility of enabling a strain-controlled response in Si-NC ensambles.
