In this paper we compare the elastic energies obtained by tight-binding molecular dynamics simulations for several strained structures of beta -FeSi2, corresponding to the most frequent epitaxial relationships 'on' and 'in' silicon. Our results confirm that, for coherent interfaces, the very common beta -FeSi2(101) or (110)//Si(111) orientation generates a very large contribution to the elastic energy, due to the large misfit. Therefore, we suggest that the frequent nucleation of such epitaxial relationships in precipitates is provided by the correspondence of the two-dimensional crystal structure for the Si sites between Si(111) and beta -FeSi2(101) or (110). We show it to be maintained even after misfit relaxation in the silicon matrix, as simulated by a large-scale molecular dynamics run.