  Quantum Monte Carlo (QMC) methods have been used to obtain accurate
binding-energy data for pairs of parallel thin metallic wires and layers
modeled by 1D and 2D homogeneous electron gases. We compare our QMC binding
energies with results obtained within the random phase approximation, finding
significant quantitative differences and disagreement over the asymptotic
behavior for bilayers at low densities. We have calculated pair-correlation
functions for metallic biwire and bilayer systems. Our QMC data could be used
to investigate van der Waals energy functionals.
