What do we know about wave function nodes?

Although quantum Monte Carlo is, in principal, an exact method for solving the Schroedinger equation, it is well-known that systems of Fermions still pose a challenge. Thus far all solutions to the "sign problem" remain inefficient (or wrong). The fixed-node approach, however, is efficient, and in many situations remains the best approach. If only we could find the exact nodes, or at least a systematic way to improve the nodes, we would, in effect, bypass the sign problem. Unfortunately, very little is known about wave function nodes, and a systematic study has never been attempted, despite the obvious consequences for improving quantum simulations that such knowledge might generate. In this paper we study the nodal surfaces of simple atomic systems.