The damage produced by primary knock-on atoms (PKA) in W has been investigated from the threshold displacement energy (TDE) where it produces one Self Interstitial Atom (SIA) – vacancy pair to larger energies, up to 100 keV, where a large molten volume is formed. The TDE has been determined in different crystal directions using the Born Oppenheimer Density Functional Molecular Dynamics (DFT-MD). A significant difference has been observed without and with the semi-core electrons. Classical MD (MD) has been used with two different empirical potentials characterized as “soft” and “hard” to obtain statistics on TDEs. Cascades of larger energy have been calculated, with these potentials, using a model that accounts for electronic losses [1]. Two other sets of cascades have been produced using the Binary Collision Approximation (BCA): a Monte Carlo BCA using SDTrimSP [2] (similar to SRIM [3]) and MARLOWE [4]. The comparison of these sets of cascades gave a recombination distance equal to 12 Å which is significantly larger from the one we reported in [5] because, here, we used bulk cascades whereas surface cascades, which produce more defects [6,7]. Investigations on the defect clustering aspect showed that the difference between BCA and MD cascades is considerably reduced after the annealing of the cascade debris at 473 K using our Object Kinetic Monte Carlo model, LAKIMOCA [8].