Quantum Monte Carlo studies of two-electron atoms constrained in spherical boxes

As part of their continuing study of the influence of the environment on the properties of atoms and molecules, the authors calculate the ground-state energies of three two-electron atoms and ions-H-, He and Li+-constrained at the centre of a hard spherical cavity. The calculations are performed using the techniques of quantum Monte Carlo (QMC); the particular QMC algorithm employed is unique in that the associated timestep error is quadratic, rather than linear, and thus yields highly accurate energies, a typical error bound being +or-0.0003 Hartree. This accuracy exceeds that previously obtained in studies employing self-consistent field Hartree-Fock and configuration interaction methods.