The nonionizing energy loss (NIEL) concept, intro-1 duced more than 40 years ago, is still used to characterize 2 the damage generated by different particles and γ -rays. Its 3 continuing relevance is due to the experimentally established 4 scaling in the creation rate of defects by radiation of different 5 types. NIEL calculations are quite simple, based on classical 6 physics. We thus name them classical NIEL, NIEL c . Their 7 calculation depends on an a priori known E d -displacement 8 threshold energy in monoatomic materials. For the compound 9 semiconductor materials studied here, GaX and InX, where X 10 are the cations N, P, As, Sb, the experimental E d values vary 11 over a wide range and only approximate values for NIEL c can 12 be calculated. Thanks to some recent studies carried out using 13 the molecular dynamic (MD) method, the NIEL values were 14 estimated using atomic scale calculations. Consequently, we can 15 now compare NIEL c with more precise data. These data also 16 include the "dynamic" behavior of the NIEL, which is related to 17 the annealing of the damage (like Frenkel pair recombination) 18 and the generation of extended crystalline defects. The NIEL 19 calculated using the MD method is referred to in the literature 20 as NIEL eff . A detailed comparison between NIEL c and NIEL eff as 21 a function of electron and proton energies is made here. It shows 22 that the difference between the two quantities is not large and 23 cannot influence the dependence of NIEL on temperature and 24 different radiation types. Both yield similar results in calculating 25 the effect of displacement damage. As an additional use of NIEL c , 26 we analyze its application to estimate the relative tolerance of 27 the different members of the GaX and InX families to radiation 28 defects as a function of particle energies. 29 Index Terms-Displacement damage, effects below damage 30 threshold, molecular dynamics (MDs), nonionizing energy loss 31 (NIEL), proton and electron interactions in III-V compound 32 semiconductors. 33 on classical physics and experimentally verified characteris-38 tics of radiation interaction with matter. We thus name it 39 classical NIEL (NIEL c ). Unfortunately, NIEL by itself does 40 not characterize the radiation-induced defects and their spatial 41 structure, which affect the electrical and optical properties of 42 the damaged materials. But, as shown in [1], it is a good 43