  The implementation and reliability of a quadratic diffusion Monte Carlo
method for the study of ground-state properties of atoms are discussed. We show
in the simple yet non-trivial calculation of the binding energy of the Li atom
that the method presented is effectively second-order in the time step. The
fulfilment of the expected quadratic behavior relies on some basic requirements
of the trial wave function used for importance sampling, in the context of the
fixed-node approximation. Expectation values of radial operators are calculated
by means of a pure estimation based on the forward walking methodology. It is
shown that accurate results without extrapolation errors can be obtained with a
pure algorithm that can be easily implemented in any previous diffusion Monte
Carlo program.
