Ac. Cosentini et al., Phase separation in the two-dimensional Hubbard model: A fixed-node quantum Monte Carlo study, PHYS REV B, 58(22), 1998, pp. R14685-R14688
Fixed-node Green's-function Monte Carlo calculations have been performed fo
r very large 16x16 two-dimensional Hubbard lattices, large interaction stre
ngths U=10,20, and 40, and many (15 similar to 20) densities between empty
and half-filling. The nodes were fixed by a simple Slater-Gutzwiller trial
wave function. For each value of U we obtained a sequence of ground-state e
nergies which is consistent with the possibility of a phase separation clos
e to half-filling, with a hole density in the hole-rich phase which is a de
creasing function of U. The energies suffer, however, from a fixed-node bia
s: more accurate nodes are needed to confirm this picture. Our extensive nu
merical results and their test against size, shell, shape, and boundary-con
dition effects also suggest that phase separation is quite a delicate issue
, on which simulations based on smaller lattices than considered here are u
nlikely to give reliable predictions.