Effects of three-body and backflow correlations in the two-dimensional electron gas

We investigate the effects of three-body and backflow correlations on ground-state properties of the two-dimensional electron gas by both variational and fixed-node Greens function Monte Carlo methods. It is found that the backflow effect is dominant over the three-body effect at high density (rs1) while they are of equal importance at the lowest density considered (rs20). With these correlations, we find significant improvements in both variational and fixed-node energies over the Slater-Jastrow results which consider only two-body correlation. The effects are comparable to those in bulk He3. We present an analytic expression for the correlation energy of the two-dimensional electron gas as a function of the density.