This thesis deals with the calculation of the plasmonic properties of metallic nano-particles. One part deals with the application of well established methods to the simulation of experiments involving spheroidal silver nano-particles. These particles can be transformed in a well defined manner using laser irradiation. The simulation results are used to support the model of the transformation process. The other part of the thesis deals with the simulation of electron microscopy experiments. Both, electron energy loss spectroscopy, as well as cathodoluminescence spectroscopy can be used to study the plasmonic properties of even single nano-particles in experiments. We extend two Maxwell-solvers to be applicable to the simulations of such experiments, the T-Matrix Method and the Discontinuous Galerkin Time-Domain method. Results for both, particle shapes of theoretical interest, as well as shapes inspired by experiments are presented and also compared against experimental results.