  We report variational and diffusion Quantum Monte Carlo ground-state energies
of the three-dimensional electron gas using a model periodic Coulomb
interaction and backflow corrections for N=54, 102, 178, and 226 electrons. We
remove finite-size effects by extrapolation and we find lower energies than
previously reported. Using the Hellman-Feynman operator sampling method
introduced in Phys. Rev. Lett. 99, 126406 (2007), we compute accurately, within
the fixed-node pproximation, the separate kinetic and interaction contributions
to the total ground-state energy. The difference between the interaction
energies obtained from the original Slater-determinant nodes and the
backflow-displaced nodes is found to be considerably larger than the difference
between the corresponding kinetic energies.

Materials Science