Effective molecular polarizabilities in some aromatic hydrocarbon crystals

Two equivalent methods of calculating effective molecular polarizabilities from crystal electric susceptibilities are compared. For monoclinic crystals containing two molecules per unit cell, there is no unique solution. The range of solutions is examined for naphthalene, anthracene, biphenyl, p-terphenyl and phenanthrene, treated as polarizable points. For all these molecules the largest polarizability component is unacceptable, owing to the point molecule approximation. When the interactions between molecules are calculated as averages between aromatic rings, more realistic polarizabilities result, showing variations consistent with the molecular geometry. Comparable results are obtained for benzene (orthorhombic). It is concluded that reliable polarizabilities should become available by developments of such an approach.