  The many-body diffusion quantum Monte Carlo (DMC) method with twist-averaged
boundary conditions is used to calculate the ground-state equation of state and
the energetics of point defects in fcc aluminum using supercells up to 1331
atoms. The DMC equilibrium lattice constant differs from experiment by 0.008 A,
or 0.2%, while the cohesive energy using DMC with backflow wave functions with
improved nodal surfaces differs by 27 meV. DMC-calculated defect formation and
migration energies agree with available experimental data, except for the
nearest-neighbor divacancy, which is found to be energetically unstable, in
agreement with previous density functional theory (DFT) calculations. DMC and
DFT calculations of vacancy defects are in reasonably close agreement.
Self-interstitial formation energies have larger differences between DMC and
DFT, of up to 0.33eV, at the tetrahedral site. We also computed formation
energies of helium interstitial defects where energies differed by up to
0.34eV, also at the tetrahedral site. The close agreement with available
experiments demonstrates that DMC can be used as a predictive method to obtain
benchmark energetics of defects in metals.
