  We extend the density matrix renormalization group to compute exact ground
states of continuum many-electron systems in one dimension with long-range
interactions. We find the exact ground state of a chain of 100 strongly
correlated artificial hydrogen atoms. The method can be used to simulate 1d
cold atom systems and to study density functional theory in an exact setting.
To illustrate, we find an interacting, extended system which is an insulator
but whose Kohn-Sham system is metallic.
