However, this approach should be used with great caution for several reasons. For instance, it does not account for any thermally activated recombination of damage, nor the well known fact that in metals the damage production is for high energies only something like 20% of the Kinchin-Pease prediction. Moreover, this approach only predicts the damage production as if all defects were isolated Frenkel pairs, while in reality in many cases collision cascades produce defect clusters or even dislocations as the initial damage state. BCA codes can, however, be extended with damage clustering and recombination models that improve on their reliability in this respect. Finally, the average threshold displacement energy is not very accurately known in most materials.