I will discuss the nodal structure of wave functions
in general and of single-particle approximation based
wave functions in particular, and ts relevance to QMC
simulations. In particular I will show that  the nodal
structures of atomic wave functions based on a product
of spatial orbitals, namely Restricted, Unrestricted,
and Generalized Valence Bond wave functions, are
equivalent. This result is verified by fixed node-diffusion
Monte Carlo simulations for atoms up to Ne. Also for a
molecular system, Li2 at the equilibrium geometry, a
multideterminantal GVB wave function does not improve
the nodal surfaces of a RHF wave function