The Particle Field Interaction, Relativistic Interface combines the Charged Particle Tracing, Electrostatics, and Magnetic Fields interfaces to model relativistic beams of charged particles that can create significant space charge density and current density distributions in the domains that contain the particles. The space charge density may, in turn, exert a significant electric force on the particles, whereas the current density contributes to the magnetic field in the surrounding domains, exerting a magnetic force on the particles.