In this paper, the main characteristics of Frank–Read (F–R) sources used in a mechanism-based discrete dislocation plasticity (M-DDP) analysis are estimated by employing a recently developed non-singular continuum elastic theory of dislocations. The critical nucleation stress, τ_nuc, is determined more accurately because the dislocation core effects are considered precisely by atomistically-informing the dislocation dynamics simulations. The nucleation time is calculated and compared with the previous predictions. The dependence of the drag coefficient of dislocations on dislocation line orientation, which affects the nucleation time and also the shape of the emitted dislocation loop, is considered. In M-DDP simulations, τ_nuc used for sources is calculated based on the assumption of an infinite domain. In reality, however, the critical nucleation stress is affected by other F–R sources. It is proposed in this paper that the critical nucleation stress should be modified by considering the effects of other dislocation sources. To this end, τ_nuc should be determined for an F–R source in a finite cell with periodic boundary conditions.