Table 3.

Performance of the fit-polar, fit-esp, final and the current AMOEBA sets of polarizability parameters on the ESP and molecular polarizability sets. Root mean square error (RMSE, in kcal/mol/e for ESP and in ų for polarizability) and unsigned mean percentage error (UMPE, defined in Eq. 3) are reported.

Parameters	ESP set (316 probing structures)		Polarizability set a,b (7284 molecules)
fit-polar	RMSE	0.0347	RMSE (αii)	0.79
			UMPE (αii)	4.5%
			RMSE (αiso)	0.39
			UMPE (αiso)	2.6%
fit-esp	RMSE	0.0326	RMSE (αii)	0.81
			UMPE (αii)	4.2%
			RMSE (αiso)	0.43
			UMPE (αiso)	2.6%
final	RMSE	0.0333	RMSE (αii)	0.79
			UMPE (αii)	4.2%
			RMSE (αiso)	0.40
			UMPE (αiso)	2.5%
AMOEBA	RMSE	0.0451	RMSE (αii)	1.54
			UMPE (αii)	8.8%
			RMSE (αiso)	1.24
			UMPE (αiso)	9.3%

^a.α_ii: statistics based on three eigenvalues, where $i=x,y,z$.

^b.α_iso: statistics based on the isotropic polarizabilities, i.e., $\frac{1}{3}\left({\alpha }_{xx}+{\alpha }_{yy}+{\alpha }_{zz}\right)$.