Theory of electrical properties of molecular crystal surfaces

Crystals inevitably have surfaces, near which crystal properties inevitably change. Quantitative changes in magnitude occur because of the loss of interactions near the surface, and qualitative changes in symmetry occur because of the loss of symmetry across the surface. This paper discusses the theory of some surface electrical properties of molecular crystals. All the properties depend on dipolar interactions between the molecules. The interactions are conveniently summed over planes of molecules parallel to the surface, when it is found that interactions between neighbouring planes are generally negligible. This result facilitates computation of surface properties. Applications discussed include surface electric fields, polarization and pyroelectricity, charge-carrier energetics, and nonlinear optics.