  Plasmonic nano antennas are highly attractive at optical frequencies due to
their strong resonances - even when their size is smaller than the wavelength -
and because of their potential of extreme field enhancement. Such antennas may
be applied for sensing of biological nano particles as well as for single
molecule detection. Because of considerable material losses and strong
dispersion of metals at optical frequencies, the numerical analysis of
plasmonic antennas is very demanding. An additional difficulty is caused when
very narrow gaps between nano particles are utilized for increasing the field
enhancement. In this paper we discuss the main difficulties of time domain
solvers, namely FDTD and FVTD and we compare various frequency domain solvers,
namely the commercial FEM packages JCMsuite, Comsol, HFSS,and Microwave Studio
with the semi-analytic MMP code that may be used as a reference due to its fast
convergence and high accuracy.
