It was noted that, in those hexagonal metals having the highest c/a ratio, experimental observations tended not to agree with the theoretical models of extended defects. In the case of Zn and Cd, a semi-empirical tight-binding method was developed for the calculation of the energy of extended defects. It was then possible to obtain a good correlation for polytypes or basal stacking faults. In the case of the (10▪2) twin, two possible interfaces were shown to be stable; in agreement with available experimental results for Zn.Twinning and Extended Defects in HCP Metals with Large c/a Ratio - Modelling and Microscopic Observations. A.Béré, T.Braisaz, P.Ruterana, G.Nouet: Physica Status Solidi A, 2005, 202[15], 2900-11