In order to evaluate the quality of the CP 3 , its ability to reproduce a full quantum-mechanical EP was investigated on a number of test systems. This was done with three sets of increasingly complex test molecules starting with simple tripeptides, over a set of small proteins, and ending with a larger insulin protein. The quality was measured by computing the rootmean-square deviation (RMSD) between the quantum-mechanical EP and the CP 3 -based EP.