Energy calculations have been carried out in order to describe the epitaxial growth of chlorinated Cu-phthalocyanine on the (001) KCl surface. The atomic coordinates in the crystal cell and the net charge distribution in the molecule are presented. The total potential energy, as well as the electrostatic (Coulomb and induced dipolar) and dispersion-repulsive contributions have been calculated for a single molecule with different orientations. It is minimal when the molecule is parallel to the substrate. There is a long plateau of the energy distribution in a wide range of θ, where θ is the angle between the molecular plane and the substrate surface. Adsorption energies for crystals with different epitaxial relations, which have been observed experimentally, are also presented. Their molecular origins are discussed.