  We report on Li-6 calculations performed with the IT-NCSM and compare them to
full NCSM calculations. We employ the Entem and Machleidt chiral two-body N3LO
interaction (regulated at 500 MeV/c), which has been modified to a phase-shift
equivalent potential by the similarity renormalization group (SRG) procedure.
We investigate the dependence of the procedure on the technique employed to
extrapolate to the complete Nmax space, the harmonic oscillator energy, and
investigate the dependence on the momentum-decoupling scale (\lambda) used in
the SRG. We also investigate the use of one or several reference states from
which the truncated basis is constructed. We find that the uncertainties
generated from various extrapolating functions used to extrapolate to the
complete Nmax space increase as Nmax increases. The extrapolation uncertainties
range from a few keV for the smallest Nmax spaces to about 50 keV for the
largest Nmax spaces. We note that the difference between extrapolated IT-NCSM
and NCSM ground-state energies, however, can be as large as a 100-250 keV
depending on the chosen harmonic oscillator energy. We also present the
extrapolation of IT-NCSM results to Nmax infinity and compare these to
similarly extrapolated full NCSM results.
