Quantum Monte Carlo calculations of nuclei with A<=7

We report quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with A less than or equal to 7 using a realistic Hamiltonian containing the Argonne upsilon(18) two-nucleon and Urbana IX three-nucleon potentials. A detailed description of the Green's-function Monte Carlo algorithm for systems with state-dependent potentials is given and a number of tests of its convergence and accuracy are performed. We find that the Hamiltonian being used results in ground states of both Li-6 and Li-7 that are stable against breakup into subclusters, but somewhat underbound compared to experiment. We also have results for He-6, He-7, and their isobaric analogs. The known excitation spectra of all these nuclei are reproduced reasonably well and we predict a number of excited states in He-6 and He-7. We also present spin-polarized one-body and several different two-body density distributions. These are the first microscopic calculations that directly produce nuclear shell structure from realistic interactions that fit NAI scattering data.