Figure 3. Validation of EEM models by comparing EEM atomic charges against QM atomic charges.

Statistical descriptors comprising the average correlation coefficient (R_avg), the average root mean square deviation (RMSD_avg) and the average absolute difference (D_avg) are given. These descriptors quantify the agreement between EEM model charges and QM charges for molecules belonging to the reference sets RS1 and RS2, and for five further test molecules T1–T5. All quantities are given in elementary charges (1 e∼1.602×10⁻¹⁹ coulombs). The names of the parameter sets encode the reference set and atom classification scheme based on which they were developed (RS1-E, RS1-EX, RS2-E, RS2-EX). Good agreement between QM and EEM charges was found for all data sets, as R_avg is close to 1, and RMSD_avg and D_avg are minimal. Calibrations that used the coarse atom type classification ‘E’ gave a similarly good agreement as those where the more detailed classification scheme ‘EX’ was used.