The multipactor effect is characterized by a very fast growth of the electronic population in vacuum Radio-Frequency (RF) devices. As it limits the transmitted RF power and can severely damage RF systems, multipactor has been subject to an extensive research for the past decades. Simulation tools are relatively accurate for the simplest cases, but less reliable for advanced problems: presence of an external magnetic field, complex geometry, time or temperature-dependent materials properties, etc. A code simulating the multipactor within an infinite parallel-plate waveguide with a dielectric coating on the bottom plate has been developed. The inclusion of a realistic energy distribution for the secondary electrons and a new emission model shows a strong dependence of the multipactor threshold on the metal work function and on the dielectric electric charge.