The authors present a first principles approach for investigating the dielectric properties of Cu-phthalocyanine (CuPc). The local position-dependent dielectric constant of CuPc oligomers is determined from the charge density induced by an external finite electric field. The dielectric constants of a CuPc monomer along and perpendicular to its plane are extracted from appropriately chosen periodic arrangements of CuPc oligomers. The authors obtain dielectric constant values of about 15 along the CuPc plane and about 3.4 perpendicular to the plane.
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External electric field along the ± directions are applied purely due to numerical reasons and is most applicable for asymmetric situations. In the present case, since the system is symmetric along the directions, the induced charge density along the direction can be obtained from that along the direction purely from symmetry.
This choice of was motivated by the fact that CuPc oligomers tend to stack with interplanar distance of about , indicating that this distance can be viewed as the effective thickness of a CuPc layer.
