The many-body diffusion quantum Monte Carlo method with twist-averaged boundary conditions was used to calculate the ground-state equation of state and the energetics of point defects in fcc aluminum using super-cells with up to 1331 atoms. The diffusion quantum Monte Carlo equilibrium lattice constant differed from experiment by 0.008Å, or 0.2%, while the cohesive energy using diffusion quantum Monte Carlo with back-flow wave functions with improved nodal surfaces differed by 27meV. Diffusion quantum Monte Carlo-calculated defect formation and migration energies agreed with available experimental data, except for the nearest-neighbor divacancy, which was found to be energetically unstable, in agreement with previous density functional theory calculations. Diffusion quantum Monte Carlo and density functional theory calculations of vacancy defects were in reasonably close agreement. Self-interstitial formation energies had larger differences between diffusion quantum Monte Carlo and density functional theory, of up to 0.33eV, at the tetrahedral site. Also computed were the 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 demonstrated that diffusion quantum Monte Carlo methods could be used as a predictive method to obtain benchmark energetics of defects in metals.

Diffusion Quantum Monte Carlo Study of the Equation of State and Point Defects in Aluminum. R.Q.Hood, P.R.C.Kent, F.A.Reboredo: Physical Review B, 2012, 85[13], 134109