In the Next-to-Minimal Supersymmetric Standard Model (NMSSM), three new particles appear: a new CP-even Higgs boson (code 45), a new CP-odd Higgs boson (code 46), and an additional neutralino (code 1000045), where the particle codes are the ones tentatively adopted by the SUSY Les Houches Accord (SLHA) community [All06].
PYTHIA does not contain any internal machinery for doing calculations in the NMSSM. Thus, the basic scattering processes should be generated by an external program (e.g. COMPHEP/CALCHEP [Puk99]) and handed to PYTHIA via the Les Houches Accord interface for parton-level events (LHA). This should then be combined with either setting the NMSSM resonance decays by hand, or by reading in an SLHA decay table prepared by an external decay package (e.g. NMHDECAY [Ell05]). One possible chain of steps for generating fully simulated events for the NMSSM, starting from a high-scale model definition, would thus be (see e.g. [Puk05]):