  We perform coupled-cluster and diffusion Monte Carlo calculations of the
energies of circular quantum dots up to 20 electrons. The coupled-cluster
calculations include triples corrections and a renormalized Coulomb interaction
defined for a given number of low-lying oscillator shells. Using such a
renormalized Coulomb interaction brings the coupled-cluster calculations with
triples correlations in excellent agreement with the diffusion Monte Carlo
calculations. This opens up perspectives for doing ab initio calculations for
much larger systems of electrons.
