Figure 2.

The EPIC model behavior is explored for Cl₂. The average polarizability (a) and the anisotropy (b) isolines (in a.u.) are plotted as a function of the Cl atomic radius, used to define the vdW surface, and the value of the inner dielectric. The target Cl₂ B3LYP values are 31.43 (average) and 18.24 (anisotropy) (c.f. Table 1). The polarizability tensor error function $(2\mid {\alpha }_{\perp }^{QM}-{\alpha }_{\perp }^{\mathit{EPIC}}\mid +\mid {\alpha }_{\left|\right|}^{QM}-{\alpha }_{\left|\right|}^{\mathit{EPIC}}\mid )/3{\alpha }_{\mathit{avg}}^{QM}$ isolines in (c) identify the regions where the EPIC model matches the B3LYP polarizability tensor. The external dielectric is set to one and the inter-nuclear distance of Cl₂ is fixed at 2.05Å. These figures show that a high dielectric value is required to match the QM anisotropy, and that a number of minima can be found on the error hypersurface.