Cu phthalocyanine (CuPc) based composites are expected to display high dielectric constants, of the order of several hundreds, based on recent experimental work. In an attempt to determine whether CuPc has a high dielectric constant intrinsically, and if so, in order to identify the circumstances under which such high dielectric constants could result, a systematic ab initio study is undertaken. This study extends prior work on the intrinsic dielectric properties of isolated CuPc and the closely related ${\mathrm{H}}_2$ phthalocyanine $\left({\mathrm{H}}_2\mathrm{Pc}\right)$ monomers. The tendency of CuPc and ${\mathrm{H}}_2\mathrm{Pc}$ monomers and polymeric sheets to stack is critically assessed, and the concomitant changes in the electronic and optical properties as a function of the stacking distance are determined. Our results indicate that both CuPc and ${\mathrm{H}}_2\mathrm{Pc}$ systems exhibit an insulator to metal transition as the stacking distance approaches $3\mathrm{\AA }$ (the equilibrium spacing). Consistent with this behavior, the dielectric constant reaches large values as the stacking distance approaches $3\mathrm{\AA }$, while it is small for larger stacking distances, in accord with our prior estimates.

• Received 1 January 2007

DOI:https://doi.org/10.1103/PhysRevB.75.155429