Microscopic calculation of surface linear optical response in crystals of para-nitroaniline

Previous theoretical results for surface linear optical response in molecular crystals are extended to treat response to the external applied field, the bulk macroscopic field, and the surface macroscopic field. They are used to calculate planewise dipole sums, surface local electric fields, surface linear susceptibilities, and surface refractive indices for surfaces normal to the [001] and [101] directions of the centrosymmetric para-nitroaniline crystals. For each direction, two different terminations give different results. Surface effects are stronger normal to the surface for the [001] direction, and in the surface for the [101] direction. Surface effects decrease sharply into the bulk, being negligible beyond neighboring layers of molecules. The present results provide input for calculations of surface-induced quadratic nonlinear optical response, reported in the following article.