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This paper deals with the passage from discrete to continuous in modeling the static elastic properties of vertical screw dislocations in a cylindrical crystal, in the setting of antiplanar linear elasticity. We study, in the framework of -convergence, the asymptotic behavior of the elastic stored energy induced by dislocations as the atomic scale tends to zero, in the regime of dilute dislocations, i.e., rescaling the energy functionals by . First we consider a continuum model, where the atomic scale is introduced as an internal scale, usually called core radius. Then we focus on a purely discrete model. In both cases, we prove that the asymptotic elastic energy as is essentially given by the number of dislocations present in the crystal. More precisely the energy per unit volume is proportional to the length of the dislocation lines, so that our result recovers in the limit as , a line tension model.