The final validation test is performed on the insulin protein, which is more than twice the size of the largest of the smaller proteins. This system is challenging also for some Kohn-Sham density functional approximations. It has been used previously in a study of the MFCC-based LoProp potentials where it was shown that a very good accuracy could be reached as long as polarizable potentials are used. Here we use the same reference as in those two studies (DEC-MP2/cc-pVDZ) to evaluate the performance of the CP 3 .