Computation of electrostatic fields in low-symmetry systems: Application to STM configurations

When complex molecules are placed in interaction with a low-symmetry physical system, an electrostatic field confined at the nanometer scale arises in a region located around the particles. It is the case in scanning tunneling microscopy (STM), where these long-range interactions modify the intrinsic electrostatic field structure and, thereby, affect the magnitude of the cohesive forces between each adsorbed particles. We present a numerical approach of this problem within the framework of the held-propagator method. Starting from the knowledge of the field distribution associated with a highly symmetrical system (a pair of metallic plane electrodes, for example), we derive the self-consistent field distribution for the whole system by introducing a generalized field propagator obtained by solving a sequence of Dyson's equations numerically. The application of this numerical scheme to electrostatic herd calculations inside a STM junction is studied in detail.